// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/read_write.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/slab.h>
#include <linux/stat.h>
#include <linux/sched/xacct.h>
#include <linux/fcntl.h>
#include <linux/file.h>
#include <linux/uio.h>
#include <linux/fsnotify.h>
#include <linux/security.h>
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/pagemap.h>
#include <linux/splice.h>
#include <linux/compat.h>
#include <linux/mount.h>
#include <linux/fs.h>
#include <linux/filelock.h>
#include "internal.h"

#include <linux/uaccess.h>
#include <asm/unistd.h>

const struct file_operations generic_ro_fops = {
        .llseek         = generic_file_llseek,
        .read_iter      = generic_file_read_iter,
        .mmap_prepare   = generic_file_readonly_mmap_prepare,
        .splice_read    = filemap_splice_read,
        .setlease       = generic_setlease,
};

EXPORT_SYMBOL(generic_ro_fops);

static inline bool unsigned_offsets(struct file *file)
{
        return file->f_op->fop_flags & FOP_UNSIGNED_OFFSET;
}

/**
 * vfs_setpos_cookie - update the file offset for lseek and reset cookie
 * @file:       file structure in question
 * @offset:     file offset to seek to
 * @maxsize:    maximum file size
 * @cookie:     cookie to reset
 *
 * Update the file offset to the value specified by @offset if the given
 * offset is valid and it is not equal to the current file offset and
 * reset the specified cookie to indicate that a seek happened.
 *
 * Return the specified offset on success and -EINVAL on invalid offset.
 */
static loff_t vfs_setpos_cookie(struct file *file, loff_t offset,
                                loff_t maxsize, u64 *cookie)
{
        if (offset < 0 && !unsigned_offsets(file))
                return -EINVAL;
        if (offset > maxsize)
                return -EINVAL;

        if (offset != file->f_pos) {
                file->f_pos = offset;
                if (cookie)
                        *cookie = 0;
        }
        return offset;
}

/**
 * vfs_setpos - update the file offset for lseek
 * @file:       file structure in question
 * @offset:     file offset to seek to
 * @maxsize:    maximum file size
 *
 * This is a low-level filesystem helper for updating the file offset to
 * the value specified by @offset if the given offset is valid and it is
 * not equal to the current file offset.
 *
 * Return the specified offset on success and -EINVAL on invalid offset.
 */
loff_t vfs_setpos(struct file *file, loff_t offset, loff_t maxsize)
{
        return vfs_setpos_cookie(file, offset, maxsize, NULL);
}
EXPORT_SYMBOL(vfs_setpos);

/**
 * must_set_pos - check whether f_pos has to be updated
 * @file: file to seek on
 * @offset: offset to use
 * @whence: type of seek operation
 * @eof: end of file
 *
 * Check whether f_pos needs to be updated and update @offset according
 * to @whence.
 *
 * Return: 0 if f_pos doesn't need to be updated, 1 if f_pos has to be
 * updated, and negative error code on failure.
 */
static int must_set_pos(struct file *file, loff_t *offset, int whence, loff_t eof)
{
        switch (whence) {
        case SEEK_END:
                *offset += eof;
                break;
        case SEEK_CUR:
                /*
                 * Here we special-case the lseek(fd, 0, SEEK_CUR)
                 * position-querying operation.  Avoid rewriting the "same"
                 * f_pos value back to the file because a concurrent read(),
                 * write() or lseek() might have altered it
                 */
                if (*offset == 0) {
                        *offset = file->f_pos;
                        return 0;
                }
                break;
        case SEEK_DATA:
                /*
                 * In the generic case the entire file is data, so as long as
                 * offset isn't at the end of the file then the offset is data.
                 */
                if ((unsigned long long)*offset >= eof)
                        return -ENXIO;
                break;
        case SEEK_HOLE:
                /*
                 * There is a virtual hole at the end of the file, so as long as
                 * offset isn't i_size or larger, return i_size.
                 */
                if ((unsigned long long)*offset >= eof)
                        return -ENXIO;
                *offset = eof;
                break;
        }

        return 1;
}

/**
 * generic_file_llseek_size - generic llseek implementation for regular files
 * @file:       file structure to seek on
 * @offset:     file offset to seek to
 * @whence:     type of seek
 * @maxsize:    max size of this file in file system
 * @eof:        offset used for SEEK_END position
 *
 * This is a variant of generic_file_llseek that allows passing in a custom
 * maximum file size and a custom EOF position, for e.g. hashed directories
 *
 * Synchronization:
 * SEEK_SET and SEEK_END are unsynchronized (but atomic on 64bit platforms)
 * SEEK_CUR is synchronized against other SEEK_CURs, but not read/writes.
 * read/writes behave like SEEK_SET against seeks.
 */
loff_t
generic_file_llseek_size(struct file *file, loff_t offset, int whence,
                loff_t maxsize, loff_t eof)
{
        int ret;

        ret = must_set_pos(file, &offset, whence, eof);
        if (ret < 0)
                return ret;
        if (ret == 0)
                return offset;

        if (whence == SEEK_CUR) {
                /*
                 * If the file requires locking via f_pos_lock we know
                 * that mutual exclusion for SEEK_CUR on the same file
                 * is guaranteed. If the file isn't locked, we take
                 * f_lock to protect against f_pos races with other
                 * SEEK_CURs.
                 */
                if (file_seek_cur_needs_f_lock(file)) {
                        guard(spinlock)(&file->f_lock);
                        return vfs_setpos(file, file->f_pos + offset, maxsize);
                }
                return vfs_setpos(file, file->f_pos + offset, maxsize);
        }

        return vfs_setpos(file, offset, maxsize);
}
EXPORT_SYMBOL(generic_file_llseek_size);

/**
 * generic_llseek_cookie - versioned llseek implementation
 * @file:       file structure to seek on
 * @offset:     file offset to seek to
 * @whence:     type of seek
 * @cookie:     cookie to update
 *
 * See generic_file_llseek for a general description and locking assumptions.
 *
 * In contrast to generic_file_llseek, this function also resets a
 * specified cookie to indicate a seek took place.
 */
loff_t generic_llseek_cookie(struct file *file, loff_t offset, int whence,
                             u64 *cookie)
{
        struct inode *inode = file->f_mapping->host;
        loff_t maxsize = inode->i_sb->s_maxbytes;
        loff_t eof = i_size_read(inode);
        int ret;

        if (WARN_ON_ONCE(!cookie))
                return -EINVAL;

        /*
         * Require that this is only used for directories that guarantee
         * synchronization between readdir and seek so that an update to
         * @cookie is correctly synchronized with concurrent readdir.
         */
        if (WARN_ON_ONCE(!(file->f_mode & FMODE_ATOMIC_POS)))
                return -EINVAL;

        ret = must_set_pos(file, &offset, whence, eof);
        if (ret < 0)
                return ret;
        if (ret == 0)
                return offset;

        /* No need to hold f_lock because we know that f_pos_lock is held. */
        if (whence == SEEK_CUR)
                return vfs_setpos_cookie(file, file->f_pos + offset, maxsize, cookie);

        return vfs_setpos_cookie(file, offset, maxsize, cookie);
}
EXPORT_SYMBOL(generic_llseek_cookie);

/**
 * generic_file_llseek - generic llseek implementation for regular files
 * @file:       file structure to seek on
 * @offset:     file offset to seek to
 * @whence:     type of seek
 *
 * This is a generic implementation of ->llseek useable for all normal local
 * filesystems.  It just updates the file offset to the value specified by
 * @offset and @whence.
 */
loff_t generic_file_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file->f_mapping->host;

        return generic_file_llseek_size(file, offset, whence,
                                        inode->i_sb->s_maxbytes,
                                        i_size_read(inode));
}
EXPORT_SYMBOL(generic_file_llseek);

/**
 * fixed_size_llseek - llseek implementation for fixed-sized devices
 * @file:       file structure to seek on
 * @offset:     file offset to seek to
 * @whence:     type of seek
 * @size:       size of the file
 *
 */
loff_t fixed_size_llseek(struct file *file, loff_t offset, int whence, loff_t size)
{
        switch (whence) {
        case SEEK_SET: case SEEK_CUR: case SEEK_END:
                return generic_file_llseek_size(file, offset, whence,
                                                size, size);
        default:
                return -EINVAL;
        }
}
EXPORT_SYMBOL(fixed_size_llseek);

/**
 * no_seek_end_llseek - llseek implementation for fixed-sized devices
 * @file:       file structure to seek on
 * @offset:     file offset to seek to
 * @whence:     type of seek
 *
 */
loff_t no_seek_end_llseek(struct file *file, loff_t offset, int whence)
{
        switch (whence) {
        case SEEK_SET: case SEEK_CUR:
                return generic_file_llseek_size(file, offset, whence,
                                                OFFSET_MAX, 0);
        default:
                return -EINVAL;
        }
}
EXPORT_SYMBOL(no_seek_end_llseek);

/**
 * no_seek_end_llseek_size - llseek implementation for fixed-sized devices
 * @file:       file structure to seek on
 * @offset:     file offset to seek to
 * @whence:     type of seek
 * @size:       maximal offset allowed
 *
 */
loff_t no_seek_end_llseek_size(struct file *file, loff_t offset, int whence, loff_t size)
{
        switch (whence) {
        case SEEK_SET: case SEEK_CUR:
                return generic_file_llseek_size(file, offset, whence,
                                                size, 0);
        default:
                return -EINVAL;
        }
}
EXPORT_SYMBOL(no_seek_end_llseek_size);

/**
 * noop_llseek - No Operation Performed llseek implementation
 * @file:       file structure to seek on
 * @offset:     file offset to seek to
 * @whence:     type of seek
 *
 * This is an implementation of ->llseek useable for the rare special case when
 * userspace expects the seek to succeed but the (device) file is actually not
 * able to perform the seek. In this case you use noop_llseek() instead of
 * falling back to the default implementation of ->llseek.
 */
loff_t noop_llseek(struct file *file, loff_t offset, int whence)
{
        return file->f_pos;
}
EXPORT_SYMBOL(noop_llseek);

loff_t default_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file_inode(file);
        loff_t retval;

        retval = inode_lock_killable(inode);
        if (retval)
                return retval;
        switch (whence) {
                case SEEK_END:
                        offset += i_size_read(inode);
                        break;
                case SEEK_CUR:
                        if (offset == 0) {
                                retval = file->f_pos;
                                goto out;
                        }
                        offset += file->f_pos;
                        break;
                case SEEK_DATA:
                        /*
                         * In the generic case the entire file is data, so as
                         * long as offset isn't at the end of the file then the
                         * offset is data.
                         */
                        if (offset >= inode->i_size) {
                                retval = -ENXIO;
                                goto out;
                        }
                        break;
                case SEEK_HOLE:
                        /*
                         * There is a virtual hole at the end of the file, so
                         * as long as offset isn't i_size or larger, return
                         * i_size.
                         */
                        if (offset >= inode->i_size) {
                                retval = -ENXIO;
                                goto out;
                        }
                        offset = inode->i_size;
                        break;
        }
        retval = -EINVAL;
        if (offset >= 0 || unsigned_offsets(file)) {
                if (offset != file->f_pos)
                        file->f_pos = offset;
                retval = offset;
        }
out:
        inode_unlock(inode);
        return retval;
}
EXPORT_SYMBOL(default_llseek);

loff_t vfs_llseek(struct file *file, loff_t offset, int whence)
{
        if (!(file->f_mode & FMODE_LSEEK))
                return -ESPIPE;
        return file->f_op->llseek(file, offset, whence);
}
EXPORT_SYMBOL(vfs_llseek);

static off_t ksys_lseek(unsigned int fd, off_t offset, unsigned int whence)
{
        off_t retval;
        CLASS(fd_pos, f)(fd);
        if (fd_empty(f))
                return -EBADF;

        retval = -EINVAL;
        if (whence <= SEEK_MAX) {
                loff_t res = vfs_llseek(fd_file(f), offset, whence);
                retval = res;
                if (res != (loff_t)retval)
                        retval = -EOVERFLOW;    /* LFS: should only happen on 32 bit platforms */
        }
        return retval;
}

SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
{
        return ksys_lseek(fd, offset, whence);
}

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE3(lseek, unsigned int, fd, compat_off_t, offset, unsigned int, whence)
{
        return ksys_lseek(fd, offset, whence);
}
#endif

#if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT) || \
        defined(__ARCH_WANT_SYS_LLSEEK)
SYSCALL_DEFINE5(llseek, unsigned int, fd, unsigned long, offset_high,
                unsigned long, offset_low, loff_t __user *, result,
                unsigned int, whence)
{
        int retval;
        CLASS(fd_pos, f)(fd);
        loff_t offset;

        if (fd_empty(f))
                return -EBADF;

        if (whence > SEEK_MAX)
                return -EINVAL;

        offset = vfs_llseek(fd_file(f), ((loff_t) offset_high << 32) | offset_low,
                        whence);

        retval = (int)offset;
        if (offset >= 0) {
                retval = -EFAULT;
                if (!copy_to_user(result, &offset, sizeof(offset)))
                        retval = 0;
        }
        return retval;
}
#endif

int rw_verify_area(int read_write, struct file *file, const loff_t *ppos, size_t count)
{
        int mask = read_write == READ ? MAY_READ : MAY_WRITE;
        int ret;

        if (unlikely((ssize_t) count < 0))
                return -EINVAL;

        if (ppos) {
                loff_t pos = *ppos;

                if (unlikely(pos < 0)) {
                        if (!unsigned_offsets(file))
                                return -EINVAL;
                        if (count >= -pos) /* both values are in 0..LLONG_MAX */
                                return -EOVERFLOW;
                } else if (unlikely((loff_t) (pos + count) < 0)) {
                        if (!unsigned_offsets(file))
                                return -EINVAL;
                }
        }

        ret = security_file_permission(file, mask);
        if (ret)
                return ret;

        return fsnotify_file_area_perm(file, mask, ppos, count);
}
EXPORT_SYMBOL(rw_verify_area);

static ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
{
        struct kiocb kiocb;
        struct iov_iter iter;
        ssize_t ret;

        init_sync_kiocb(&kiocb, filp);
        kiocb.ki_pos = (ppos ? *ppos : 0);
        iov_iter_ubuf(&iter, ITER_DEST, buf, len);

        ret = filp->f_op->read_iter(&kiocb, &iter);
        BUG_ON(ret == -EIOCBQUEUED);
        if (ppos)
                *ppos = kiocb.ki_pos;
        return ret;
}

static int warn_unsupported(struct file *file, const char *op)
{
        pr_warn_ratelimited(
                "kernel %s not supported for file %pD4 (pid: %d comm: %.20s)\n",
                op, file, current->pid, current->comm);
        return -EINVAL;
}

ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
{
        struct kvec iov = {
                .iov_base       = buf,
                .iov_len        = min_t(size_t, count, MAX_RW_COUNT),
        };
        struct kiocb kiocb;
        struct iov_iter iter;
        ssize_t ret;

        if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))
                return -EINVAL;
        if (!(file->f_mode & FMODE_CAN_READ))
                return -EINVAL;
        /*
         * Also fail if ->read_iter and ->read are both wired up as that
         * implies very convoluted semantics.
         */
        if (unlikely(!file->f_op->read_iter || file->f_op->read))
                return warn_unsupported(file, "read");

        init_sync_kiocb(&kiocb, file);
        kiocb.ki_pos = pos ? *pos : 0;
        iov_iter_kvec(&iter, ITER_DEST, &iov, 1, iov.iov_len);
        ret = file->f_op->read_iter(&kiocb, &iter);
        if (ret > 0) {
                if (pos)
                        *pos = kiocb.ki_pos;
                fsnotify_access(file);
                add_rchar(current, ret);
        }
        inc_syscr(current);
        return ret;
}

ssize_t kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
{
        ssize_t ret;

        ret = rw_verify_area(READ, file, pos, count);
        if (ret)
                return ret;
        return __kernel_read(file, buf, count, pos);
}
EXPORT_SYMBOL(kernel_read);

ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
{
        ssize_t ret;

        if (!(file->f_mode & FMODE_READ))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_READ))
                return -EINVAL;
        if (unlikely(!access_ok(buf, count)))
                return -EFAULT;

        ret = rw_verify_area(READ, file, pos, count);
        if (ret)
                return ret;
        if (count > MAX_RW_COUNT)
                count =  MAX_RW_COUNT;

        if (file->f_op->read)
                ret = file->f_op->read(file, buf, count, pos);
        else if (file->f_op->read_iter)
                ret = new_sync_read(file, buf, count, pos);
        else
                ret = -EINVAL;
        if (ret > 0) {
                fsnotify_access(file);
                add_rchar(current, ret);
        }
        inc_syscr(current);
        return ret;
}

static ssize_t new_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos)
{
        struct kiocb kiocb;
        struct iov_iter iter;
        ssize_t ret;

        init_sync_kiocb(&kiocb, filp);
        kiocb.ki_pos = (ppos ? *ppos : 0);
        iov_iter_ubuf(&iter, ITER_SOURCE, (void __user *)buf, len);

        ret = filp->f_op->write_iter(&kiocb, &iter);
        BUG_ON(ret == -EIOCBQUEUED);
        if (ret > 0 && ppos)
                *ppos = kiocb.ki_pos;
        return ret;
}

/* caller is responsible for file_start_write/file_end_write */
ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos)
{
        struct kiocb kiocb;
        ssize_t ret;

        if (WARN_ON_ONCE(!(file->f_mode & FMODE_WRITE)))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_WRITE))
                return -EINVAL;
        /*
         * Also fail if ->write_iter and ->write are both wired up as that
         * implies very convoluted semantics.
         */
        if (unlikely(!file->f_op->write_iter || file->f_op->write))
                return warn_unsupported(file, "write");

        init_sync_kiocb(&kiocb, file);
        kiocb.ki_pos = pos ? *pos : 0;
        ret = file->f_op->write_iter(&kiocb, from);
        if (ret > 0) {
                if (pos)
                        *pos = kiocb.ki_pos;
                fsnotify_modify(file);
                add_wchar(current, ret);
        }
        inc_syscw(current);
        return ret;
}

/* caller is responsible for file_start_write/file_end_write */
ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t *pos)
{
        struct kvec iov = {
                .iov_base       = (void *)buf,
                .iov_len        = min_t(size_t, count, MAX_RW_COUNT),
        };
        struct iov_iter iter;
        iov_iter_kvec(&iter, ITER_SOURCE, &iov, 1, iov.iov_len);
        return __kernel_write_iter(file, &iter, pos);
}
/*
 * This "EXPORT_SYMBOL_GPL()" is more of a "EXPORT_SYMBOL_DONTUSE()",
 * but autofs is one of the few internal kernel users that actually
 * wants this _and_ can be built as a module. So we need to export
 * this symbol for autofs, even though it really isn't appropriate
 * for any other kernel modules.
 */
EXPORT_SYMBOL_GPL(__kernel_write);

ssize_t kernel_write(struct file *file, const void *buf, size_t count,
                            loff_t *pos)
{
        ssize_t ret;

        ret = rw_verify_area(WRITE, file, pos, count);
        if (ret)
                return ret;

        file_start_write(file);
        ret =  __kernel_write(file, buf, count, pos);
        file_end_write(file);
        return ret;
}
EXPORT_SYMBOL(kernel_write);

ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
{
        ssize_t ret;

        if (!(file->f_mode & FMODE_WRITE))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_WRITE))
                return -EINVAL;
        if (unlikely(!access_ok(buf, count)))
                return -EFAULT;

        ret = rw_verify_area(WRITE, file, pos, count);
        if (ret)
                return ret;
        if (count > MAX_RW_COUNT)
                count =  MAX_RW_COUNT;
        file_start_write(file);
        if (file->f_op->write)
                ret = file->f_op->write(file, buf, count, pos);
        else if (file->f_op->write_iter)
                ret = new_sync_write(file, buf, count, pos);
        else
                ret = -EINVAL;
        if (ret > 0) {
                fsnotify_modify(file);
                add_wchar(current, ret);
        }
        inc_syscw(current);
        file_end_write(file);
        return ret;
}

/* file_ppos returns &file->f_pos or NULL if file is stream */
static inline loff_t *file_ppos(struct file *file)
{
        return file->f_mode & FMODE_STREAM ? NULL : &file->f_pos;
}

ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count)
{
        CLASS(fd_pos, f)(fd);
        ssize_t ret = -EBADF;

        if (!fd_empty(f)) {
                loff_t pos, *ppos = file_ppos(fd_file(f));
                if (ppos) {
                        pos = *ppos;
                        ppos = &pos;
                }
                ret = vfs_read(fd_file(f), buf, count, ppos);
                if (ret >= 0 && ppos)
                        fd_file(f)->f_pos = pos;
        }
        return ret;
}

SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
{
        return ksys_read(fd, buf, count);
}

ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count)
{
        CLASS(fd_pos, f)(fd);
        ssize_t ret = -EBADF;

        if (!fd_empty(f)) {
                loff_t pos, *ppos = file_ppos(fd_file(f));
                if (ppos) {
                        pos = *ppos;
                        ppos = &pos;
                }
                ret = vfs_write(fd_file(f), buf, count, ppos);
                if (ret >= 0 && ppos)
                        fd_file(f)->f_pos = pos;
        }

        return ret;
}

SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf,
                size_t, count)
{
        return ksys_write(fd, buf, count);
}

ssize_t ksys_pread64(unsigned int fd, char __user *buf, size_t count,
                     loff_t pos)
{
        if (pos < 0)
                return -EINVAL;

        CLASS(fd, f)(fd);
        if (fd_empty(f))
                return -EBADF;

        if (fd_file(f)->f_mode & FMODE_PREAD)
                return vfs_read(fd_file(f), buf, count, &pos);

        return -ESPIPE;
}

SYSCALL_DEFINE4(pread64, unsigned int, fd, char __user *, buf,
                        size_t, count, loff_t, pos)
{
        return ksys_pread64(fd, buf, count, pos);
}

#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_PREAD64)
COMPAT_SYSCALL_DEFINE5(pread64, unsigned int, fd, char __user *, buf,
                       size_t, count, compat_arg_u64_dual(pos))
{
        return ksys_pread64(fd, buf, count, compat_arg_u64_glue(pos));
}
#endif

ssize_t ksys_pwrite64(unsigned int fd, const char __user *buf,
                      size_t count, loff_t pos)
{
        if (pos < 0)
                return -EINVAL;

        CLASS(fd, f)(fd);
        if (fd_empty(f))
                return -EBADF;

        if (fd_file(f)->f_mode & FMODE_PWRITE)
                return vfs_write(fd_file(f), buf, count, &pos);

        return -ESPIPE;
}

SYSCALL_DEFINE4(pwrite64, unsigned int, fd, const char __user *, buf,
                         size_t, count, loff_t, pos)
{
        return ksys_pwrite64(fd, buf, count, pos);
}

#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_PWRITE64)
COMPAT_SYSCALL_DEFINE5(pwrite64, unsigned int, fd, const char __user *, buf,
                       size_t, count, compat_arg_u64_dual(pos))
{
        return ksys_pwrite64(fd, buf, count, compat_arg_u64_glue(pos));
}
#endif

static ssize_t do_iter_readv_writev(struct file *filp, struct iov_iter *iter,
                loff_t *ppos, int type, rwf_t flags)
{
        struct kiocb kiocb;
        ssize_t ret;

        init_sync_kiocb(&kiocb, filp);
        ret = kiocb_set_rw_flags(&kiocb, flags, type);
        if (ret)
                return ret;
        kiocb.ki_pos = (ppos ? *ppos : 0);

        if (type == READ)
                ret = filp->f_op->read_iter(&kiocb, iter);
        else
                ret = filp->f_op->write_iter(&kiocb, iter);
        BUG_ON(ret == -EIOCBQUEUED);
        if (ppos)
                *ppos = kiocb.ki_pos;
        return ret;
}

/* Do it by hand, with file-ops */
static ssize_t do_loop_readv_writev(struct file *filp, struct iov_iter *iter,
                loff_t *ppos, int type, rwf_t flags)
{
        ssize_t ret = 0;

        if (flags & ~RWF_HIPRI)
                return -EOPNOTSUPP;

        while (iov_iter_count(iter)) {
                ssize_t nr;

                if (type == READ) {
                        nr = filp->f_op->read(filp, iter_iov_addr(iter),
                                                iter_iov_len(iter), ppos);
                } else {
                        nr = filp->f_op->write(filp, iter_iov_addr(iter),
                                                iter_iov_len(iter), ppos);
                }

                if (nr < 0) {
                        if (!ret)
                                ret = nr;
                        break;
                }
                ret += nr;
                if (nr != iter_iov_len(iter))
                        break;
                iov_iter_advance(iter, nr);
        }

        return ret;
}

ssize_t vfs_iocb_iter_read(struct file *file, struct kiocb *iocb,
                           struct iov_iter *iter)
{
        size_t tot_len;
        ssize_t ret = 0;

        if (!file->f_op->read_iter)
                return -EINVAL;
        if (!(file->f_mode & FMODE_READ))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_READ))
                return -EINVAL;

        tot_len = iov_iter_count(iter);
        if (!tot_len)
                goto out;
        ret = rw_verify_area(READ, file, &iocb->ki_pos, tot_len);
        if (ret < 0)
                return ret;

        ret = file->f_op->read_iter(iocb, iter);
out:
        if (ret >= 0)
                fsnotify_access(file);
        return ret;
}
EXPORT_SYMBOL(vfs_iocb_iter_read);

ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos,
                      rwf_t flags)
{
        size_t tot_len;
        ssize_t ret = 0;

        if (!file->f_op->read_iter)
                return -EINVAL;
        if (!(file->f_mode & FMODE_READ))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_READ))
                return -EINVAL;

        tot_len = iov_iter_count(iter);
        if (!tot_len)
                goto out;
        ret = rw_verify_area(READ, file, ppos, tot_len);
        if (ret < 0)
                return ret;

        ret = do_iter_readv_writev(file, iter, ppos, READ, flags);
out:
        if (ret >= 0)
                fsnotify_access(file);
        return ret;
}
EXPORT_SYMBOL(vfs_iter_read);

/*
 * Caller is responsible for calling kiocb_end_write() on completion
 * if async iocb was queued.
 */
ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
                            struct iov_iter *iter)
{
        size_t tot_len;
        ssize_t ret = 0;

        if (!file->f_op->write_iter)
                return -EINVAL;
        if (!(file->f_mode & FMODE_WRITE))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_WRITE))
                return -EINVAL;

        tot_len = iov_iter_count(iter);
        if (!tot_len)
                return 0;
        ret = rw_verify_area(WRITE, file, &iocb->ki_pos, tot_len);
        if (ret < 0)
                return ret;

        kiocb_start_write(iocb);
        ret = file->f_op->write_iter(iocb, iter);
        if (ret != -EIOCBQUEUED)
                kiocb_end_write(iocb);
        if (ret > 0)
                fsnotify_modify(file);

        return ret;
}
EXPORT_SYMBOL(vfs_iocb_iter_write);

ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos,
                       rwf_t flags)
{
        size_t tot_len;
        ssize_t ret;

        if (!(file->f_mode & FMODE_WRITE))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_WRITE))
                return -EINVAL;
        if (!file->f_op->write_iter)
                return -EINVAL;

        tot_len = iov_iter_count(iter);
        if (!tot_len)
                return 0;

        ret = rw_verify_area(WRITE, file, ppos, tot_len);
        if (ret < 0)
                return ret;

        file_start_write(file);
        ret = do_iter_readv_writev(file, iter, ppos, WRITE, flags);
        if (ret > 0)
                fsnotify_modify(file);
        file_end_write(file);

        return ret;
}
EXPORT_SYMBOL(vfs_iter_write);

static ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
                         unsigned long vlen, loff_t *pos, rwf_t flags)
{
        struct iovec iovstack[UIO_FASTIOV];
        struct iovec *iov = iovstack;
        struct iov_iter iter;
        size_t tot_len;
        ssize_t ret = 0;

        if (!(file->f_mode & FMODE_READ))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_READ))
                return -EINVAL;

        ret = import_iovec(ITER_DEST, vec, vlen, ARRAY_SIZE(iovstack), &iov,
                           &iter);
        if (ret < 0)
                return ret;

        tot_len = iov_iter_count(&iter);
        if (!tot_len)
                goto out;

        ret = rw_verify_area(READ, file, pos, tot_len);
        if (ret < 0)
                goto out;

        if (file->f_op->read_iter)
                ret = do_iter_readv_writev(file, &iter, pos, READ, flags);
        else
                ret = do_loop_readv_writev(file, &iter, pos, READ, flags);
out:
        if (ret >= 0)
                fsnotify_access(file);
        kfree(iov);
        return ret;
}

static ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
                          unsigned long vlen, loff_t *pos, rwf_t flags)
{
        struct iovec iovstack[UIO_FASTIOV];
        struct iovec *iov = iovstack;
        struct iov_iter iter;
        size_t tot_len;
        ssize_t ret = 0;

        if (!(file->f_mode & FMODE_WRITE))
                return -EBADF;
        if (!(file->f_mode & FMODE_CAN_WRITE))
                return -EINVAL;

        ret = import_iovec(ITER_SOURCE, vec, vlen, ARRAY_SIZE(iovstack), &iov,
                           &iter);
        if (ret < 0)
                return ret;

        tot_len = iov_iter_count(&iter);
        if (!tot_len)
                goto out;

        ret = rw_verify_area(WRITE, file, pos, tot_len);
        if (ret < 0)
                goto out;

        file_start_write(file);
        if (file->f_op->write_iter)
                ret = do_iter_readv_writev(file, &iter, pos, WRITE, flags);
        else
                ret = do_loop_readv_writev(file, &iter, pos, WRITE, flags);
        if (ret > 0)
                fsnotify_modify(file);
        file_end_write(file);
out:
        kfree(iov);
        return ret;
}

static ssize_t do_readv(unsigned long fd, const struct iovec __user *vec,
                        unsigned long vlen, rwf_t flags)
{
        CLASS(fd_pos, f)(fd);
        ssize_t ret = -EBADF;

        if (!fd_empty(f)) {
                loff_t pos, *ppos = file_ppos(fd_file(f));
                if (ppos) {
                        pos = *ppos;
                        ppos = &pos;
                }
                ret = vfs_readv(fd_file(f), vec, vlen, ppos, flags);
                if (ret >= 0 && ppos)
                        fd_file(f)->f_pos = pos;
        }

        if (ret > 0)
                add_rchar(current, ret);
        inc_syscr(current);
        return ret;
}

static ssize_t do_writev(unsigned long fd, const struct iovec __user *vec,
                         unsigned long vlen, rwf_t flags)
{
        CLASS(fd_pos, f)(fd);
        ssize_t ret = -EBADF;

        if (!fd_empty(f)) {
                loff_t pos, *ppos = file_ppos(fd_file(f));
                if (ppos) {
                        pos = *ppos;
                        ppos = &pos;
                }
                ret = vfs_writev(fd_file(f), vec, vlen, ppos, flags);
                if (ret >= 0 && ppos)
                        fd_file(f)->f_pos = pos;
        }

        if (ret > 0)
                add_wchar(current, ret);
        inc_syscw(current);
        return ret;
}

static inline loff_t pos_from_hilo(unsigned long high, unsigned long low)
{
#define HALF_LONG_BITS (BITS_PER_LONG / 2)
        return (((loff_t)high << HALF_LONG_BITS) << HALF_LONG_BITS) | low;
}

static ssize_t do_preadv(unsigned long fd, const struct iovec __user *vec,
                         unsigned long vlen, loff_t pos, rwf_t flags)
{
        ssize_t ret = -EBADF;

        if (pos < 0)
                return -EINVAL;

        CLASS(fd, f)(fd);
        if (!fd_empty(f)) {
                ret = -ESPIPE;
                if (fd_file(f)->f_mode & FMODE_PREAD)
                        ret = vfs_readv(fd_file(f), vec, vlen, &pos, flags);
        }

        if (ret > 0)
                add_rchar(current, ret);
        inc_syscr(current);
        return ret;
}

static ssize_t do_pwritev(unsigned long fd, const struct iovec __user *vec,
                          unsigned long vlen, loff_t pos, rwf_t flags)
{
        ssize_t ret = -EBADF;

        if (pos < 0)
                return -EINVAL;

        CLASS(fd, f)(fd);
        if (!fd_empty(f)) {
                ret = -ESPIPE;
                if (fd_file(f)->f_mode & FMODE_PWRITE)
                        ret = vfs_writev(fd_file(f), vec, vlen, &pos, flags);
        }

        if (ret > 0)
                add_wchar(current, ret);
        inc_syscw(current);
        return ret;
}

SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
                unsigned long, vlen)
{
        return do_readv(fd, vec, vlen, 0);
}

SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
                unsigned long, vlen)
{
        return do_writev(fd, vec, vlen, 0);
}

SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
                unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
{
        loff_t pos = pos_from_hilo(pos_h, pos_l);

        return do_preadv(fd, vec, vlen, pos, 0);
}

SYSCALL_DEFINE6(preadv2, unsigned long, fd, const struct iovec __user *, vec,
                unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h,
                rwf_t, flags)
{
        loff_t pos = pos_from_hilo(pos_h, pos_l);

        if (pos == -1)
                return do_readv(fd, vec, vlen, flags);

        return do_preadv(fd, vec, vlen, pos, flags);
}

SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
                unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
{
        loff_t pos = pos_from_hilo(pos_h, pos_l);

        return do_pwritev(fd, vec, vlen, pos, 0);
}

SYSCALL_DEFINE6(pwritev2, unsigned long, fd, const struct iovec __user *, vec,
                unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h,
                rwf_t, flags)
{
        loff_t pos = pos_from_hilo(pos_h, pos_l);

        if (pos == -1)
                return do_writev(fd, vec, vlen, flags);

        return do_pwritev(fd, vec, vlen, pos, flags);
}

/*
 * Various compat syscalls.  Note that they all pretend to take a native
 * iovec - import_iovec will properly treat those as compat_iovecs based on
 * in_compat_syscall().
 */
#ifdef CONFIG_COMPAT
#ifdef __ARCH_WANT_COMPAT_SYS_PREADV64
COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
                const struct iovec __user *, vec,
                unsigned long, vlen, loff_t, pos)
{
        return do_preadv(fd, vec, vlen, pos, 0);
}
#endif

COMPAT_SYSCALL_DEFINE5(preadv, compat_ulong_t, fd,
                const struct iovec __user *, vec,
                compat_ulong_t, vlen, u32, pos_low, u32, pos_high)
{
        loff_t pos = ((loff_t)pos_high << 32) | pos_low;

        return do_preadv(fd, vec, vlen, pos, 0);
}

#ifdef __ARCH_WANT_COMPAT_SYS_PREADV64V2
COMPAT_SYSCALL_DEFINE5(preadv64v2, unsigned long, fd,
                const struct iovec __user *, vec,
                unsigned long, vlen, loff_t, pos, rwf_t, flags)
{
        if (pos == -1)
                return do_readv(fd, vec, vlen, flags);
        return do_preadv(fd, vec, vlen, pos, flags);
}
#endif

COMPAT_SYSCALL_DEFINE6(preadv2, compat_ulong_t, fd,
                const struct iovec __user *, vec,
                compat_ulong_t, vlen, u32, pos_low, u32, pos_high,
                rwf_t, flags)
{
        loff_t pos = ((loff_t)pos_high << 32) | pos_low;

        if (pos == -1)
                return do_readv(fd, vec, vlen, flags);
        return do_preadv(fd, vec, vlen, pos, flags);
}

#ifdef __ARCH_WANT_COMPAT_SYS_PWRITEV64
COMPAT_SYSCALL_DEFINE4(pwritev64, unsigned long, fd,
                const struct iovec __user *, vec,
                unsigned long, vlen, loff_t, pos)
{
        return do_pwritev(fd, vec, vlen, pos, 0);
}
#endif

COMPAT_SYSCALL_DEFINE5(pwritev, compat_ulong_t, fd,
                const struct iovec __user *,vec,
                compat_ulong_t, vlen, u32, pos_low, u32, pos_high)
{
        loff_t pos = ((loff_t)pos_high << 32) | pos_low;

        return do_pwritev(fd, vec, vlen, pos, 0);
}

#ifdef __ARCH_WANT_COMPAT_SYS_PWRITEV64V2
COMPAT_SYSCALL_DEFINE5(pwritev64v2, unsigned long, fd,
                const struct iovec __user *, vec,
                unsigned long, vlen, loff_t, pos, rwf_t, flags)
{
        if (pos == -1)
                return do_writev(fd, vec, vlen, flags);
        return do_pwritev(fd, vec, vlen, pos, flags);
}
#endif

COMPAT_SYSCALL_DEFINE6(pwritev2, compat_ulong_t, fd,
                const struct iovec __user *,vec,
                compat_ulong_t, vlen, u32, pos_low, u32, pos_high, rwf_t, flags)
{
        loff_t pos = ((loff_t)pos_high << 32) | pos_low;

        if (pos == -1)
                return do_writev(fd, vec, vlen, flags);
        return do_pwritev(fd, vec, vlen, pos, flags);
}
#endif /* CONFIG_COMPAT */

static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
                           size_t count, loff_t max)
{
        struct inode *in_inode, *out_inode;
        struct pipe_inode_info *opipe;
        loff_t pos;
        loff_t out_pos;
        ssize_t retval;
        int fl;

        /*
         * Get input file, and verify that it is ok..
         */
        CLASS(fd, in)(in_fd);
        if (fd_empty(in))
                return -EBADF;
        if (!(fd_file(in)->f_mode & FMODE_READ))
                return -EBADF;
        if (!ppos) {
                pos = fd_file(in)->f_pos;
        } else {
                pos = *ppos;
                if (!(fd_file(in)->f_mode & FMODE_PREAD))
                        return -ESPIPE;
        }
        retval = rw_verify_area(READ, fd_file(in), &pos, count);
        if (retval < 0)
                return retval;
        if (count > MAX_RW_COUNT)
                count =  MAX_RW_COUNT;

        /*
         * Get output file, and verify that it is ok..
         */
        CLASS(fd, out)(out_fd);
        if (fd_empty(out))
                return -EBADF;
        if (!(fd_file(out)->f_mode & FMODE_WRITE))
                return -EBADF;
        in_inode = file_inode(fd_file(in));
        out_inode = file_inode(fd_file(out));
        out_pos = fd_file(out)->f_pos;

        if (!max)
                max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);

        if (unlikely(pos + count > max)) {
                if (pos >= max)
                        return -EOVERFLOW;
                count = max - pos;
        }

        fl = 0;
#if 0
        /*
         * We need to debate whether we can enable this or not. The
         * man page documents EAGAIN return for the output at least,
         * and the application is arguably buggy if it doesn't expect
         * EAGAIN on a non-blocking file descriptor.
         */
        if (fd_file(in)->f_flags & O_NONBLOCK)
                fl = SPLICE_F_NONBLOCK;
#endif
        opipe = get_pipe_info(fd_file(out), true);
        if (!opipe) {
                retval = rw_verify_area(WRITE, fd_file(out), &out_pos, count);
                if (retval < 0)
                        return retval;
                retval = do_splice_direct(fd_file(in), &pos, fd_file(out), &out_pos,
                                          count, fl);
        } else {
                if (fd_file(out)->f_flags & O_NONBLOCK)
                        fl |= SPLICE_F_NONBLOCK;

                retval = splice_file_to_pipe(fd_file(in), opipe, &pos, count, fl);
        }

        if (retval > 0) {
                add_rchar(current, retval);
                add_wchar(current, retval);
                fsnotify_access(fd_file(in));
                fsnotify_modify(fd_file(out));
                fd_file(out)->f_pos = out_pos;
                if (ppos)
                        *ppos = pos;
                else
                        fd_file(in)->f_pos = pos;
        }

        inc_syscr(current);
        inc_syscw(current);
        if (pos > max)
                retval = -EOVERFLOW;
        return retval;
}

SYSCALL_DEFINE4(sendfile, int, out_fd, int, in_fd, off_t __user *, offset, size_t, count)
{
        loff_t pos;
        off_t off;
        ssize_t ret;

        if (offset) {
                if (unlikely(get_user(off, offset)))
                        return -EFAULT;
                pos = off;
                ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
                if (unlikely(put_user(pos, offset)))
                        return -EFAULT;
                return ret;
        }

        return do_sendfile(out_fd, in_fd, NULL, count, 0);
}

SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd, loff_t __user *, offset, size_t, count)
{
        loff_t pos;
        ssize_t ret;

        if (offset) {
                if (unlikely(copy_from_user(&pos, offset, sizeof(loff_t))))
                        return -EFAULT;
                ret = do_sendfile(out_fd, in_fd, &pos, count, 0);
                if (unlikely(put_user(pos, offset)))
                        return -EFAULT;
                return ret;
        }

        return do_sendfile(out_fd, in_fd, NULL, count, 0);
}

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE4(sendfile, int, out_fd, int, in_fd,
                compat_off_t __user *, offset, compat_size_t, count)
{
        loff_t pos;
        off_t off;
        ssize_t ret;

        if (offset) {
                if (unlikely(get_user(off, offset)))
                        return -EFAULT;
                pos = off;
                ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
                if (unlikely(put_user(pos, offset)))
                        return -EFAULT;
                return ret;
        }

        return do_sendfile(out_fd, in_fd, NULL, count, 0);
}

COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
                compat_loff_t __user *, offset, compat_size_t, count)
{
        loff_t pos;
        ssize_t ret;

        if (offset) {
                if (unlikely(copy_from_user(&pos, offset, sizeof(loff_t))))
                        return -EFAULT;
                ret = do_sendfile(out_fd, in_fd, &pos, count, 0);
                if (unlikely(put_user(pos, offset)))
                        return -EFAULT;
                return ret;
        }

        return do_sendfile(out_fd, in_fd, NULL, count, 0);
}
#endif

/*
 * Performs necessary checks before doing a file copy
 *
 * Can adjust amount of bytes to copy via @req_count argument.
 * Returns appropriate error code that caller should return or
 * zero in case the copy should be allowed.
 */
static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
                                    struct file *file_out, loff_t pos_out,
                                    size_t *req_count, unsigned int flags)
{
        struct inode *inode_in = file_inode(file_in);
        struct inode *inode_out = file_inode(file_out);
        uint64_t count = *req_count;
        loff_t size_in;
        int ret;

        ret = generic_file_rw_checks(file_in, file_out);
        if (ret)
                return ret;

        /*
         * We allow some filesystems to handle cross sb copy, but passing
         * a file of the wrong filesystem type to filesystem driver can result
         * in an attempt to dereference the wrong type of ->private_data, so
         * avoid doing that until we really have a good reason.
         *
         * nfs and cifs define several different file_system_type structures
         * and several different sets of file_operations, but they all end up
         * using the same ->copy_file_range() function pointer.
         */
        if (flags & COPY_FILE_SPLICE) {
                /* cross sb splice is allowed */
        } else if (file_out->f_op->copy_file_range) {
                if (file_in->f_op->copy_file_range !=
                    file_out->f_op->copy_file_range)
                        return -EXDEV;
        } else if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb) {
                return -EXDEV;
        }

        /* Don't touch certain kinds of inodes */
        if (IS_IMMUTABLE(inode_out))
                return -EPERM;

        if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out))
                return -ETXTBSY;

        /* Ensure offsets don't wrap. */
        if (pos_in + count < pos_in || pos_out + count < pos_out)
                return -EOVERFLOW;

        /* Shorten the copy to EOF */
        size_in = i_size_read(inode_in);
        if (pos_in >= size_in)
                count = 0;
        else
                count = min(count, size_in - (uint64_t)pos_in);

        ret = generic_write_check_limits(file_out, pos_out, &count);
        if (ret)
                return ret;

        /* Don't allow overlapped copying within the same file. */
        if (inode_in == inode_out &&
            pos_out + count > pos_in &&
            pos_out < pos_in + count)
                return -EINVAL;

        *req_count = count;
        return 0;
}

/*
 * copy_file_range() differs from regular file read and write in that it
 * specifically allows return partial success.  When it does so is up to
 * the copy_file_range method.
 */
ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
                            struct file *file_out, loff_t pos_out,
                            size_t len, unsigned int flags)
{
        ssize_t ret;
        bool splice = flags & COPY_FILE_SPLICE;
        bool samesb = file_inode(file_in)->i_sb == file_inode(file_out)->i_sb;

        if (flags & ~COPY_FILE_SPLICE)
                return -EINVAL;

        ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len,
                                       flags);
        if (unlikely(ret))
                return ret;

        ret = rw_verify_area(READ, file_in, &pos_in, len);
        if (unlikely(ret))
                return ret;

        ret = rw_verify_area(WRITE, file_out, &pos_out, len);
        if (unlikely(ret))
                return ret;

        if (len == 0)
                return 0;

        /*
         * Make sure return value doesn't overflow in 32bit compat mode.  Also
         * limit the size for all cases except when calling ->copy_file_range().
         */
        if (splice || !file_out->f_op->copy_file_range || in_compat_syscall())
                len = min_t(size_t, MAX_RW_COUNT, len);

        file_start_write(file_out);

        /*
         * Cloning is supported by more file systems, so we implement copy on
         * same sb using clone, but for filesystems where both clone and copy
         * are supported (e.g. nfs,cifs), we only call the copy method.
         */
        if (!splice && file_out->f_op->copy_file_range) {
                ret = file_out->f_op->copy_file_range(file_in, pos_in,
                                                      file_out, pos_out,
                                                      len, flags);
        } else if (!splice && file_in->f_op->remap_file_range && samesb) {
                ret = file_in->f_op->remap_file_range(file_in, pos_in,
                                file_out, pos_out, len, REMAP_FILE_CAN_SHORTEN);
                /* fallback to splice */
                if (ret <= 0)
                        splice = true;
        } else if (samesb) {
                /* Fallback to splice for same sb copy for backward compat */
                splice = true;
        }

        file_end_write(file_out);

        if (!splice)
                goto done;

        /*
         * We can get here for same sb copy of filesystems that do not implement
         * ->copy_file_range() in case filesystem does not support clone or in
         * case filesystem supports clone but rejected the clone request (e.g.
         * because it was not block aligned).
         *
         * In both cases, fall back to kernel copy so we are able to maintain a
         * consistent story about which filesystems support copy_file_range()
         * and which filesystems do not, that will allow userspace tools to
         * make consistent desicions w.r.t using copy_file_range().
         *
         * We also get here if caller (e.g. nfsd) requested COPY_FILE_SPLICE
         * for server-side-copy between any two sb.
         *
         * In any case, we call do_splice_direct() and not splice_file_range(),
         * without file_start_write() held, to avoid possible deadlocks related
         * to splicing from input file, while file_start_write() is held on
         * the output file on a different sb.
         */
        ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out, len, 0);
done:
        if (ret > 0) {
                fsnotify_access(file_in);
                add_rchar(current, ret);
                fsnotify_modify(file_out);
                add_wchar(current, ret);
        }

        inc_syscr(current);
        inc_syscw(current);

        return ret;
}
EXPORT_SYMBOL(vfs_copy_file_range);

SYSCALL_DEFINE6(copy_file_range, int, fd_in, loff_t __user *, off_in,
                int, fd_out, loff_t __user *, off_out,
                size_t, len, unsigned int, flags)
{
        loff_t pos_in;
        loff_t pos_out;
        ssize_t ret = -EBADF;

        CLASS(fd, f_in)(fd_in);
        if (fd_empty(f_in))
                return -EBADF;

        CLASS(fd, f_out)(fd_out);
        if (fd_empty(f_out))
                return -EBADF;

        if (off_in) {
                if (copy_from_user(&pos_in, off_in, sizeof(loff_t)))
                        return -EFAULT;
        } else {
                pos_in = fd_file(f_in)->f_pos;
        }

        if (off_out) {
                if (copy_from_user(&pos_out, off_out, sizeof(loff_t)))
                        return -EFAULT;
        } else {
                pos_out = fd_file(f_out)->f_pos;
        }

        if (flags != 0)
                return -EINVAL;

        ret = vfs_copy_file_range(fd_file(f_in), pos_in, fd_file(f_out), pos_out, len,
                                  flags);
        if (ret > 0) {
                pos_in += ret;
                pos_out += ret;

                if (off_in) {
                        if (copy_to_user(off_in, &pos_in, sizeof(loff_t)))
                                ret = -EFAULT;
                } else {
                        fd_file(f_in)->f_pos = pos_in;
                }

                if (off_out) {
                        if (copy_to_user(off_out, &pos_out, sizeof(loff_t)))
                                ret = -EFAULT;
                } else {
                        fd_file(f_out)->f_pos = pos_out;
                }
        }
        return ret;
}

/*
 * Don't operate on ranges the page cache doesn't support, and don't exceed the
 * LFS limits.  If pos is under the limit it becomes a short access.  If it
 * exceeds the limit we return -EFBIG.
 */
int generic_write_check_limits(struct file *file, loff_t pos, loff_t *count)
{
        struct inode *inode = file->f_mapping->host;
        loff_t max_size = inode->i_sb->s_maxbytes;
        loff_t limit = rlimit(RLIMIT_FSIZE);

        if (limit != RLIM_INFINITY) {
                if (pos >= limit) {
                        send_sig(SIGXFSZ, current, 0);
                        return -EFBIG;
                }
                *count = min(*count, limit - pos);
        }

        if (!(file->f_flags & O_LARGEFILE))
                max_size = MAX_NON_LFS;

        if (unlikely(pos >= max_size))
                return -EFBIG;

        *count = min(*count, max_size - pos);

        return 0;
}
EXPORT_SYMBOL_GPL(generic_write_check_limits);

/* Like generic_write_checks(), but takes size of write instead of iter. */
int generic_write_checks_count(struct kiocb *iocb, loff_t *count)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;

        if (IS_SWAPFILE(inode))
                return -ETXTBSY;

        if (!*count)
                return 0;

        if (iocb->ki_flags & IOCB_APPEND)
                iocb->ki_pos = i_size_read(inode);

        if ((iocb->ki_flags & IOCB_NOWAIT) &&
            !((iocb->ki_flags & IOCB_DIRECT) ||
              (file->f_op->fop_flags & FOP_BUFFER_WASYNC)))
                return -EINVAL;

        return generic_write_check_limits(iocb->ki_filp, iocb->ki_pos, count);
}
EXPORT_SYMBOL(generic_write_checks_count);

/*
 * Performs necessary checks before doing a write
 *
 * Can adjust writing position or amount of bytes to write.
 * Returns appropriate error code that caller should return or
 * zero in case that write should be allowed.
 */
ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
{
        loff_t count = iov_iter_count(from);
        int ret;

        ret = generic_write_checks_count(iocb, &count);
        if (ret)
                return ret;

        iov_iter_truncate(from, count);
        return iov_iter_count(from);
}
EXPORT_SYMBOL(generic_write_checks);

/*
 * Performs common checks before doing a file copy/clone
 * from @file_in to @file_out.
 */
int generic_file_rw_checks(struct file *file_in, struct file *file_out)
{
        struct inode *inode_in = file_inode(file_in);
        struct inode *inode_out = file_inode(file_out);

        /* Don't copy dirs, pipes, sockets... */
        if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
                return -EISDIR;
        if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
                return -EINVAL;

        if (!(file_in->f_mode & FMODE_READ) ||
            !(file_out->f_mode & FMODE_WRITE) ||
            (file_out->f_flags & O_APPEND))
                return -EBADF;

        return 0;
}

int generic_atomic_write_valid(struct kiocb *iocb, struct iov_iter *iter)
{
        size_t len = iov_iter_count(iter);

        if (!iter_is_ubuf(iter))
                return -EINVAL;

        if (!is_power_of_2(len))
                return -EINVAL;

        if (!IS_ALIGNED(iocb->ki_pos, len))
                return -EINVAL;

        if (!(iocb->ki_flags & IOCB_DIRECT))
                return -EOPNOTSUPP;

        return 0;
}
EXPORT_SYMBOL_GPL(generic_atomic_write_valid);