fs/backing-file.c - linux - Git at Google

 // 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_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 backing_aio {
 	struct kiocb iocb;
 	refcount_t ref;
 	struct kiocb *orig_iocb;
 	/* used for aio completion */
 	void (*end_write)(struct file *);
 	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;

 	if (aio->end_write)
 		aio->end_write(orig_iocb->ki_filp);

 	orig_iocb->ki_pos = iocb->ki_pos;
 	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);
 }


 ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
 			       struct kiocb *iocb, int flags,
 			       struct backing_file_ctx *ctx)
 {
 	struct backing_aio *aio = NULL;
 	const struct cred *old_cred;
 	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;

 	old_cred = override_creds(ctx->cred);
 	if (is_sync_kiocb(iocb)) {
 		rwf_t rwf = iocb_to_rw_flags(flags);

 		ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
 	} else {
 		ret = -ENOMEM;
 		aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
 		if (!aio)
 			goto out;

 		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);
 	}
 out:
 	revert_creds(old_cred);

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

 	return ret;
 }
 EXPORT_SYMBOL_GPL(backing_file_read_iter);

 ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
 				struct kiocb *iocb, int flags,
 				struct backing_file_ctx *ctx)
 {
 	const struct cred *old_cred;
 	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(ctx->user_file);
 	if (ret)
 		return ret;

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

 	/*
 	 * Stacked filesystems don't support deferred completions, don't copy
 	 * this property in case it is set by the issuer.
 	 */
 	flags &= ~IOCB_DIO_CALLER_COMP;

 	old_cred = override_creds(ctx->cred);
 	if (is_sync_kiocb(iocb)) {
 		rwf_t rwf = iocb_to_rw_flags(flags);

 		ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf);
 		if (ctx->end_write)
 			ctx->end_write(ctx->user_file);
 	} else {
 		struct backing_aio *aio;

 		ret = backing_aio_init_wq(iocb);
 		if (ret)
 			goto out;

 		ret = -ENOMEM;
 		aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
 		if (!aio)
 			goto out;

 		aio->orig_iocb = iocb;
 		aio->end_write = ctx->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);
 	}
 out:
 	revert_creds(old_cred);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(backing_file_write_iter);

 ssize_t backing_file_splice_read(struct file *in, loff_t *ppos,
 				 struct pipe_inode_info *pipe, size_t len,
 				 unsigned int flags,
 				 struct backing_file_ctx *ctx)
 {
 	const struct cred *old_cred;
 	ssize_t ret;

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

 	old_cred = override_creds(ctx->cred);
 	ret = vfs_splice_read(in, ppos, pipe, len, flags);
 	revert_creds(old_cred);

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

 	return ret;
 }
 EXPORT_SYMBOL_GPL(backing_file_splice_read);

 ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
 				  struct file *out, loff_t *ppos, size_t len,
 				  unsigned int flags,
 				  struct backing_file_ctx *ctx)
 {
 	const struct cred *old_cred;
 	ssize_t ret;

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

 	ret = file_remove_privs(ctx->user_file);
 	if (ret)
 		return ret;

 	old_cred = override_creds(ctx->cred);
 	file_start_write(out);
 	ret = iter_file_splice_write(pipe, out, ppos, len, flags);
 	file_end_write(out);
 	revert_creds(old_cred);

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

 	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)
 {
 	const struct cred *old_cred;
 	int ret;

 	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||
 	    WARN_ON_ONCE(ctx->user_file != vma->vm_file))
 		return -EIO;

 	if (!file->f_op->mmap)
 		return -ENODEV;

 	vma_set_file(vma, file);

 	old_cred = override_creds(ctx->cred);
 	ret = call_mmap(vma->vm_file, vma);
 	revert_creds(old_cred);

 	if (ctx->accessed)
 		ctx->accessed(ctx->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);
	// 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_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 backing_aio {
	struct kiocb iocb;
	refcount_t ref;
	struct kiocb *orig_iocb;
	/* used for aio completion */
	void (end_write)(struct file );
	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;

	if (aio->end_write)
	aio->end_write(orig_iocb->ki_filp);

	orig_iocb->ki_pos = iocb->ki_pos;
	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);
	}


	ssize_t backing_file_read_iter(struct file file, struct iov_iter iter,
	struct kiocb *iocb, int flags,
	struct backing_file_ctx *ctx)
	{
	struct backing_aio *aio = NULL;
	const struct cred *old_cred;
	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;

	old_cred = override_creds(ctx->cred);
	if (is_sync_kiocb(iocb)) {
	rwf_t rwf = iocb_to_rw_flags(flags);

	ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
	} else {
	ret = -ENOMEM;
	aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
	if (!aio)
	goto out;

	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);
	}
	out:
	revert_creds(old_cred);

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

	return ret;
	}
	EXPORT_SYMBOL_GPL(backing_file_read_iter);

	ssize_t backing_file_write_iter(struct file file, struct iov_iter iter,
	struct kiocb *iocb, int flags,
	struct backing_file_ctx *ctx)
	{
	const struct cred *old_cred;
	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(ctx->user_file);
	if (ret)
	return ret;

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

	/*
	* Stacked filesystems don't support deferred completions, don't copy
	* this property in case it is set by the issuer.
	*/
	flags &= ~IOCB_DIO_CALLER_COMP;

	old_cred = override_creds(ctx->cred);
	if (is_sync_kiocb(iocb)) {
	rwf_t rwf = iocb_to_rw_flags(flags);

	ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf);
	if (ctx->end_write)
	ctx->end_write(ctx->user_file);
	} else {
	struct backing_aio *aio;

	ret = backing_aio_init_wq(iocb);
	if (ret)
	goto out;

	ret = -ENOMEM;
	aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
	if (!aio)
	goto out;

	aio->orig_iocb = iocb;
	aio->end_write = ctx->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);
	}
	out:
	revert_creds(old_cred);

	return ret;
	}
	EXPORT_SYMBOL_GPL(backing_file_write_iter);

	ssize_t backing_file_splice_read(struct file in, loff_t ppos,
	struct pipe_inode_info *pipe, size_t len,
	unsigned int flags,
	struct backing_file_ctx *ctx)
	{
	const struct cred *old_cred;
	ssize_t ret;

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

	old_cred = override_creds(ctx->cred);
	ret = vfs_splice_read(in, ppos, pipe, len, flags);
	revert_creds(old_cred);

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

	return ret;
	}
	EXPORT_SYMBOL_GPL(backing_file_splice_read);

	ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
	struct file out, loff_t ppos, size_t len,
	unsigned int flags,
	struct backing_file_ctx *ctx)
	{
	const struct cred *old_cred;
	ssize_t ret;

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

	ret = file_remove_privs(ctx->user_file);
	if (ret)
	return ret;

	old_cred = override_creds(ctx->cred);
	file_start_write(out);
	ret = iter_file_splice_write(pipe, out, ppos, len, flags);
	file_end_write(out);
	revert_creds(old_cred);

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

	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)
	{
	const struct cred *old_cred;
	int ret;

	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) \|\|
	WARN_ON_ONCE(ctx->user_file != vma->vm_file))
	return -EIO;

	if (!file->f_op->mmap)
	return -ENODEV;

	vma_set_file(vma, file);

	old_cred = override_creds(ctx->cred);
	ret = call_mmap(vma->vm_file, vma);
	revert_creds(old_cred);

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