// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * file.c - operations for regular (text) files.
 *
 * Based on sysfs:
 *      sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
 *
 * configfs Copyright (C) 2005 Oracle.  All rights reserved.
 */

#include <linux/fs.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
#include <linux/uio.h>
#include <linux/configfs.h>
#include "configfs_internal.h"

/*
 * A simple attribute can only be 4096 characters.  Why 4k?  Because the
 * original code limited it to PAGE_SIZE.  That's a bad idea, though,
 * because an attribute of 16k on ia64 won't work on x86.  So we limit to
 * 4k, our minimum common page size.
 */
#define SIMPLE_ATTR_SIZE 4096

struct configfs_buffer {
        size_t                  count;
        loff_t                  pos;
        char                    * page;
        const struct configfs_item_operations   *ops;
        struct mutex            mutex;
        int                     needs_read_fill;
        bool                    read_in_progress;
        bool                    write_in_progress;
        char                    *bin_buffer;
        int                     bin_buffer_size;
        int                     cb_max_size;
        struct config_item      *item;
        struct module           *owner;
        union {
                struct configfs_attribute       *attr;
                struct configfs_bin_attribute   *bin_attr;
        };
};

static inline struct configfs_fragment *to_frag(struct file *file)
{
        struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;

        return sd->s_frag;
}

static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)
{
        struct configfs_fragment *frag = to_frag(file);
        ssize_t count = -ENOENT;

        if (!buffer->page)
                buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
        if (!buffer->page)
                return -ENOMEM;

        down_read(&frag->frag_sem);
        if (!frag->frag_dead)
                count = buffer->attr->show(buffer->item, buffer->page);
        up_read(&frag->frag_sem);

        if (count < 0)
                return count;
        if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))
                return -EIO;
        buffer->needs_read_fill = 0;
        buffer->count = count;
        return 0;
}

static ssize_t configfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct configfs_buffer *buffer = file->private_data;
        ssize_t retval = 0;

        mutex_lock(&buffer->mutex);
        if (buffer->needs_read_fill) {
                retval = fill_read_buffer(file, buffer);
                if (retval)
                        goto out;
        }
        pr_debug("%s: count = %zd, pos = %lld, buf = %s\n",
                 __func__, iov_iter_count(to), iocb->ki_pos, buffer->page);
        if (iocb->ki_pos >= buffer->count)
                goto out;
        retval = copy_to_iter(buffer->page + iocb->ki_pos,
                              buffer->count - iocb->ki_pos, to);
        iocb->ki_pos += retval;
        if (retval == 0)
                retval = -EFAULT;
out:
        mutex_unlock(&buffer->mutex);
        return retval;
}

static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct configfs_fragment *frag = to_frag(file);
        struct configfs_buffer *buffer = file->private_data;
        ssize_t retval = 0;
        ssize_t len;

        mutex_lock(&buffer->mutex);

        /* we don't support switching read/write modes */
        if (buffer->write_in_progress) {
                retval = -ETXTBSY;
                goto out;
        }
        buffer->read_in_progress = true;

        if (buffer->needs_read_fill) {
                /* perform first read with buf == NULL to get extent */
                down_read(&frag->frag_sem);
                if (!frag->frag_dead)
                        len = buffer->bin_attr->read(buffer->item, NULL, 0);
                else
                        len = -ENOENT;
                up_read(&frag->frag_sem);
                if (len <= 0) {
                        retval = len;
                        goto out;
                }

                /* do not exceed the maximum value */
                if (buffer->cb_max_size && len > buffer->cb_max_size) {
                        retval = -EFBIG;
                        goto out;
                }

                buffer->bin_buffer = vmalloc(len);
                if (buffer->bin_buffer == NULL) {
                        retval = -ENOMEM;
                        goto out;
                }
                buffer->bin_buffer_size = len;

                /* perform second read to fill buffer */
                down_read(&frag->frag_sem);
                if (!frag->frag_dead)
                        len = buffer->bin_attr->read(buffer->item,
                                                     buffer->bin_buffer, len);
                else
                        len = -ENOENT;
                up_read(&frag->frag_sem);
                if (len < 0) {
                        retval = len;
                        vfree(buffer->bin_buffer);
                        buffer->bin_buffer_size = 0;
                        buffer->bin_buffer = NULL;
                        goto out;
                }

                buffer->needs_read_fill = 0;
        }

        if (iocb->ki_pos >= buffer->bin_buffer_size)
                goto out;
        retval = copy_to_iter(buffer->bin_buffer + iocb->ki_pos,
                              buffer->bin_buffer_size - iocb->ki_pos, to);
        iocb->ki_pos += retval;
        if (retval == 0)
                retval = -EFAULT;
out:
        mutex_unlock(&buffer->mutex);
        return retval;
}

/* Fill @buffer with data coming from @from. */
static int fill_write_buffer(struct configfs_buffer *buffer,
                             struct iov_iter *from)
{
        int copied;

        if (!buffer->page)
                buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
        if (!buffer->page)
                return -ENOMEM;

        copied = copy_from_iter(buffer->page, SIMPLE_ATTR_SIZE - 1, from);
        buffer->needs_read_fill = 1;
        /* if buf is assumed to contain a string, terminate it by \0,
         * so e.g. sscanf() can scan the string easily */
        buffer->page[copied] = 0;
        return copied ? : -EFAULT;
}

static int
flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
{
        struct configfs_fragment *frag = to_frag(file);
        int res = -ENOENT;

        down_read(&frag->frag_sem);
        if (!frag->frag_dead)
                res = buffer->attr->store(buffer->item, buffer->page, count);
        up_read(&frag->frag_sem);
        return res;
}


/*
 * There is no easy way for us to know if userspace is only doing a partial
 * write, so we don't support them. We expect the entire buffer to come on the
 * first write.
 * Hint: if you're writing a value, first read the file, modify only the value
 * you're changing, then write entire buffer back.
 */
static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct configfs_buffer *buffer = file->private_data;
        int len;

        mutex_lock(&buffer->mutex);
        len = fill_write_buffer(buffer, from);
        if (len > 0)
                len = flush_write_buffer(file, buffer, len);
        if (len > 0)
                iocb->ki_pos += len;
        mutex_unlock(&buffer->mutex);
        return len;
}

static ssize_t configfs_bin_write_iter(struct kiocb *iocb,
                                       struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct configfs_buffer *buffer = file->private_data;
        void *tbuf = NULL;
        size_t end_offset;
        ssize_t len;

        mutex_lock(&buffer->mutex);

        /* we don't support switching read/write modes */
        if (buffer->read_in_progress) {
                len = -ETXTBSY;
                goto out;
        }
        buffer->write_in_progress = true;

        /* buffer grows? */
        end_offset = iocb->ki_pos + iov_iter_count(from);
        if (end_offset > buffer->bin_buffer_size) {
                if (buffer->cb_max_size && end_offset > buffer->cb_max_size) {
                        len = -EFBIG;
                        goto out;
                }

                tbuf = vmalloc(end_offset);
                if (tbuf == NULL) {
                        len = -ENOMEM;
                        goto out;
                }

                /* copy old contents */
                if (buffer->bin_buffer) {
                        memcpy(tbuf, buffer->bin_buffer,
                                buffer->bin_buffer_size);
                        vfree(buffer->bin_buffer);
                }

                /* clear the new area */
                memset(tbuf + buffer->bin_buffer_size, 0,
                        end_offset - buffer->bin_buffer_size);
                buffer->bin_buffer = tbuf;
                buffer->bin_buffer_size = end_offset;
        }

        len = copy_from_iter(buffer->bin_buffer + iocb->ki_pos,
                             buffer->bin_buffer_size - iocb->ki_pos, from);
        iocb->ki_pos += len;
out:
        mutex_unlock(&buffer->mutex);
        return len ? : -EFAULT;
}

static int __configfs_open_file(struct inode *inode, struct file *file, int type)
{
        struct dentry *dentry = file->f_path.dentry;
        struct configfs_fragment *frag = to_frag(file);
        struct configfs_attribute *attr;
        struct configfs_buffer *buffer;
        int error;

        error = -ENOMEM;
        buffer = kzalloc_obj(struct configfs_buffer);
        if (!buffer)
                goto out;

        error = -ENOENT;
        down_read(&frag->frag_sem);
        if (unlikely(frag->frag_dead))
                goto out_free_buffer;

        error = -EINVAL;
        buffer->item = to_item(dentry->d_parent);
        if (!buffer->item)
                goto out_free_buffer;

        attr = to_attr(dentry);
        if (!attr)
                goto out_free_buffer;

        if (type & CONFIGFS_ITEM_BIN_ATTR) {
                buffer->bin_attr = to_bin_attr(dentry);
                buffer->cb_max_size = buffer->bin_attr->cb_max_size;
        } else {
                buffer->attr = attr;
        }

        buffer->owner = attr->ca_owner;
        /* Grab the module reference for this attribute if we have one */
        error = -ENODEV;
        if (!try_module_get(buffer->owner))
                goto out_free_buffer;

        error = -EACCES;
        if (!buffer->item->ci_type)
                goto out_put_module;

        buffer->ops = buffer->item->ci_type->ct_item_ops;

        /* File needs write support.
         * The inode's perms must say it's ok,
         * and we must have a store method.
         */
        if (file->f_mode & FMODE_WRITE) {
                if (!(inode->i_mode & S_IWUGO))
                        goto out_put_module;
                if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
                        goto out_put_module;
                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
                        goto out_put_module;
        }

        /* File needs read support.
         * The inode's perms must say it's ok, and we there
         * must be a show method for it.
         */
        if (file->f_mode & FMODE_READ) {
                if (!(inode->i_mode & S_IRUGO))
                        goto out_put_module;
                if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
                        goto out_put_module;
                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
                        goto out_put_module;
        }

        mutex_init(&buffer->mutex);
        buffer->needs_read_fill = 1;
        buffer->read_in_progress = false;
        buffer->write_in_progress = false;
        file->private_data = buffer;
        up_read(&frag->frag_sem);
        return 0;

out_put_module:
        module_put(buffer->owner);
out_free_buffer:
        up_read(&frag->frag_sem);
        kfree(buffer);
out:
        return error;
}

static int configfs_release(struct inode *inode, struct file *filp)
{
        struct configfs_buffer *buffer = filp->private_data;

        module_put(buffer->owner);
        if (buffer->page)
                free_page((unsigned long)buffer->page);
        mutex_destroy(&buffer->mutex);
        kfree(buffer);
        return 0;
}

static int configfs_open_file(struct inode *inode, struct file *filp)
{
        return __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
}

static int configfs_open_bin_file(struct inode *inode, struct file *filp)
{
        return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
}

static int configfs_release_bin_file(struct inode *inode, struct file *file)
{
        struct configfs_buffer *buffer = file->private_data;

        if (buffer->write_in_progress) {
                struct configfs_fragment *frag = to_frag(file);

                down_read(&frag->frag_sem);
                if (!frag->frag_dead) {
                        /* result of ->release() is ignored */
                        buffer->bin_attr->write(buffer->item,
                                        buffer->bin_buffer,
                                        buffer->bin_buffer_size);
                }
                up_read(&frag->frag_sem);
        }

        vfree(buffer->bin_buffer);

        configfs_release(inode, file);
        return 0;
}


const struct file_operations configfs_file_operations = {
        .read_iter      = configfs_read_iter,
        .write_iter     = configfs_write_iter,
        .llseek         = generic_file_llseek,
        .open           = configfs_open_file,
        .release        = configfs_release,
};

const struct file_operations configfs_bin_file_operations = {
        .read_iter      = configfs_bin_read_iter,
        .write_iter     = configfs_bin_write_iter,
        .llseek         = NULL,         /* bin file is not seekable */
        .open           = configfs_open_bin_file,
        .release        = configfs_release_bin_file,
};

/**
 *      configfs_create_file - create an attribute file for an item.
 *      @item:  item we're creating for.
 *      @attr:  atrribute descriptor.
 */

int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
{
        struct dentry *dir = item->ci_dentry;
        struct configfs_dirent *parent_sd = dir->d_fsdata;
        umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
        int error = 0;

        inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
        error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
                                     CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
        inode_unlock(d_inode(dir));

        return error;
}

/**
 *      configfs_create_bin_file - create a binary attribute file for an item.
 *      @item:  item we're creating for.
 *      @bin_attr: atrribute descriptor.
 */

int configfs_create_bin_file(struct config_item *item,
                const struct configfs_bin_attribute *bin_attr)
{
        struct dentry *dir = item->ci_dentry;
        struct configfs_dirent *parent_sd = dir->d_fsdata;
        umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
        int error = 0;

        inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
        error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
                                     CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
        inode_unlock(dir->d_inode);

        return error;
}