// SPDX-License-Identifier: GPL-2.0-only
/*
 * Common helpers for stackable filesystems and backing files.
 *
 * Forked from fs/overlayfs/file.c.
 *
 * Copyright (C) 2017 Red Hat, Inc.
 * Copyright (C) 2023 CTERA Networks.
 */

#include <linux/fs.h>
#include <linux/backing-file.h>
#include <linux/splice.h>
#include <linux/mm.h>

#include "internal.h"

/**
 * backing_file_open - open a backing file for kernel internal use
 * @user_path:  path that the user reuqested to open
 * @flags:      open flags
 * @real_path:  path of the backing file
 * @cred:       credentials for open
 *
 * Open a backing file for a stackable filesystem (e.g., overlayfs).
 * @user_path may be on the stackable filesystem and @real_path on the
 * underlying filesystem.  In this case, we want to be able to return the
 * @user_path of the stackable filesystem. This is done by embedding the
 * returned file into a container structure that also stores the stacked
 * file's path, which can be retrieved using backing_file_user_path().
 */
struct file *backing_file_open(const struct path *user_path, int flags,
                               const struct path *real_path,
                               const struct cred *cred)
{
        struct file *f;
        int error;

        f = alloc_empty_backing_file(flags, cred);
        if (IS_ERR(f))
                return f;

        path_get(user_path);
        backing_file_set_user_path(f, user_path);
        error = vfs_open(real_path, f);
        if (error) {
                fput(f);
                f = ERR_PTR(error);
        }

        return f;
}
EXPORT_SYMBOL_GPL(backing_file_open);

struct file *backing_tmpfile_open(const struct path *user_path, int flags,
                                  const struct path *real_parentpath,
                                  umode_t mode, const struct cred *cred)
{
        struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt);
        struct file *f;
        int error;

        f = alloc_empty_backing_file(flags, cred);
        if (IS_ERR(f))
                return f;

        path_get(user_path);
        backing_file_set_user_path(f, user_path);
        error = vfs_tmpfile(real_idmap, real_parentpath, f, mode);
        if (error) {
                fput(f);
                f = ERR_PTR(error);
        }
        return f;
}
EXPORT_SYMBOL(backing_tmpfile_open);

struct backing_aio {
        struct kiocb iocb;
        refcount_t ref;
        struct kiocb *orig_iocb;
        /* used for aio completion */
        void (*end_write)(struct kiocb *iocb, ssize_t);
        struct work_struct work;
        long res;
};

static struct kmem_cache *backing_aio_cachep;

#define BACKING_IOCB_MASK \
        (IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND)

static rwf_t iocb_to_rw_flags(int flags)
{
        return (__force rwf_t)(flags & BACKING_IOCB_MASK);
}

static void backing_aio_put(struct backing_aio *aio)
{
        if (refcount_dec_and_test(&aio->ref)) {
                fput(aio->iocb.ki_filp);
                kmem_cache_free(backing_aio_cachep, aio);
        }
}

static void backing_aio_cleanup(struct backing_aio *aio, long res)
{
        struct kiocb *iocb = &aio->iocb;
        struct kiocb *orig_iocb = aio->orig_iocb;

        orig_iocb->ki_pos = iocb->ki_pos;
        if (aio->end_write)
                aio->end_write(orig_iocb, res);

        backing_aio_put(aio);
}

static void backing_aio_rw_complete(struct kiocb *iocb, long res)
{
        struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
        struct kiocb *orig_iocb = aio->orig_iocb;

        if (iocb->ki_flags & IOCB_WRITE)
                kiocb_end_write(iocb);

        backing_aio_cleanup(aio, res);
        orig_iocb->ki_complete(orig_iocb, res);
}

static void backing_aio_complete_work(struct work_struct *work)
{
        struct backing_aio *aio = container_of(work, struct backing_aio, work);

        backing_aio_rw_complete(&aio->iocb, aio->res);
}

static void backing_aio_queue_completion(struct kiocb *iocb, long res)
{
        struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);

        /*
         * Punt to a work queue to serialize updates of mtime/size.
         */
        aio->res = res;
        INIT_WORK(&aio->work, backing_aio_complete_work);
        queue_work(file_inode(aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq,
                   &aio->work);
}

static int backing_aio_init_wq(struct kiocb *iocb)
{
        struct super_block *sb = file_inode(iocb->ki_filp)->i_sb;

        if (sb->s_dio_done_wq)
                return 0;

        return sb_init_dio_done_wq(sb);
}

static int do_backing_file_read_iter(struct file *file, struct iov_iter *iter,
                                     struct kiocb *iocb, int flags)
{
        struct backing_aio *aio = NULL;
        int ret;

        if (is_sync_kiocb(iocb)) {
                rwf_t rwf = iocb_to_rw_flags(flags);

                return vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
        }

        aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
        if (!aio)
                return -ENOMEM;

        aio->orig_iocb = iocb;
        kiocb_clone(&aio->iocb, iocb, get_file(file));
        aio->iocb.ki_complete = backing_aio_rw_complete;
        refcount_set(&aio->ref, 2);
        ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
        backing_aio_put(aio);
        if (ret != -EIOCBQUEUED)
                backing_aio_cleanup(aio, ret);
        return ret;
}

ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
                               struct kiocb *iocb, int flags,
                               struct backing_file_ctx *ctx)
{
        ssize_t ret;

        if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
                return -EIO;

        if (!iov_iter_count(iter))
                return 0;

        if (iocb->ki_flags & IOCB_DIRECT &&
            !(file->f_mode & FMODE_CAN_ODIRECT))
                return -EINVAL;

        scoped_with_creds(ctx->cred)
                ret = do_backing_file_read_iter(file, iter, iocb, flags);

        if (ctx->accessed)
                ctx->accessed(iocb->ki_filp);

        return ret;
}
EXPORT_SYMBOL_GPL(backing_file_read_iter);

static int do_backing_file_write_iter(struct file *file, struct iov_iter *iter,
                                      struct kiocb *iocb, int flags,
                                      void (*end_write)(struct kiocb *, ssize_t))
{
        struct backing_aio *aio;
        int ret;

        if (is_sync_kiocb(iocb)) {
                rwf_t rwf = iocb_to_rw_flags(flags);

                ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf);
                if (end_write)
                        end_write(iocb, ret);
                return ret;
        }

        ret = backing_aio_init_wq(iocb);
        if (ret)
                return ret;

        aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
        if (!aio)
                return -ENOMEM;

        aio->orig_iocb = iocb;
        aio->end_write = end_write;
        kiocb_clone(&aio->iocb, iocb, get_file(file));
        aio->iocb.ki_flags = flags;
        aio->iocb.ki_complete = backing_aio_queue_completion;
        refcount_set(&aio->ref, 2);
        ret = vfs_iocb_iter_write(file, &aio->iocb, iter);
        backing_aio_put(aio);
        if (ret != -EIOCBQUEUED)
                backing_aio_cleanup(aio, ret);
        return ret;
}

ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
                                struct kiocb *iocb, int flags,
                                struct backing_file_ctx *ctx)
{
        ssize_t ret;

        if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
                return -EIO;

        if (!iov_iter_count(iter))
                return 0;

        ret = file_remove_privs(iocb->ki_filp);
        if (ret)
                return ret;

        if (iocb->ki_flags & IOCB_DIRECT &&
            !(file->f_mode & FMODE_CAN_ODIRECT))
                return -EINVAL;

        scoped_with_creds(ctx->cred)
                return do_backing_file_write_iter(file, iter, iocb, flags, ctx->end_write);
}
EXPORT_SYMBOL_GPL(backing_file_write_iter);

ssize_t backing_file_splice_read(struct file *in, struct kiocb *iocb,
                                 struct pipe_inode_info *pipe, size_t len,
                                 unsigned int flags,
                                 struct backing_file_ctx *ctx)
{
        ssize_t ret;

        if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
                return -EIO;

        scoped_with_creds(ctx->cred)
                ret = vfs_splice_read(in, &iocb->ki_pos, pipe, len, flags);

        if (ctx->accessed)
                ctx->accessed(iocb->ki_filp);

        return ret;
}
EXPORT_SYMBOL_GPL(backing_file_splice_read);

ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
                                  struct file *out, struct kiocb *iocb,
                                  size_t len, unsigned int flags,
                                  struct backing_file_ctx *ctx)
{
        ssize_t ret;

        if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
                return -EIO;

        if (!out->f_op->splice_write)
                return -EINVAL;

        ret = file_remove_privs(iocb->ki_filp);
        if (ret)
                return ret;

        scoped_with_creds(ctx->cred) {
                file_start_write(out);
                ret = out->f_op->splice_write(pipe, out, &iocb->ki_pos, len, flags);
                file_end_write(out);
        }

        if (ctx->end_write)
                ctx->end_write(iocb, ret);

        return ret;
}
EXPORT_SYMBOL_GPL(backing_file_splice_write);

int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
                      struct backing_file_ctx *ctx)
{
        struct file *user_file = vma->vm_file;
        int ret;

        if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
                return -EIO;

        if (!can_mmap_file(file))
                return -ENODEV;

        vma_set_file(vma, file);

        scoped_with_creds(ctx->cred)
                ret = vfs_mmap(vma->vm_file, vma);

        if (ctx->accessed)
                ctx->accessed(user_file);

        return ret;
}
EXPORT_SYMBOL_GPL(backing_file_mmap);

static int __init backing_aio_init(void)
{
        backing_aio_cachep = KMEM_CACHE(backing_aio, SLAB_HWCACHE_ALIGN);
        if (!backing_aio_cachep)
                return -ENOMEM;

        return 0;
}
fs_initcall(backing_aio_init);