From: Omar Sandoval <osandov@osandov.com>
To: Al Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
linux-api@vger.kernel.org, kernel-team@fb.com,
Xi Wang <xi@cs.washington.edu>
Subject: Re: [RFC PATCH v3 1/2] fs: add AT_REPLACE flag for linkat() which replaces the target
Date: Tue, 24 Apr 2018 15:14:43 -0700 [thread overview]
Message-ID: <20180424221443.GA9228@vader> (raw)
In-Reply-To: <eac9480f80c689504148b5d658ee4218cc1e421e.1524549513.git.osandov@fb.com>
On Mon, Apr 23, 2018 at 11:19:41PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
>
> One of the most common uses of temporary files is the classic atomic
> replacement pattern, i.e.,
>
> - write temporary file
> - fsync temporary file
> - rename temporary file over real file
> - fsync parent directory
>
> Now, we have O_TMPFILE, which gives us a much better way to create
> temporary files, but it's not possible to use it for this pattern.
>
> This patch introduces an AT_REPLACE flag which allows linkat() to
> replace the target file. Now, the temporary file in the pattern above
> can be a proper O_TMPFILE. Even without O_TMPFILE, this is a new
> primitive which might be useful in other contexts.
>
> The implementation on the VFS side mimics sys_renameat2().
>
> Cc: Xi Wang <xi@cs.washington.edu>
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
> fs/ecryptfs/inode.c | 2 +-
> fs/namei.c | 181 +++++++++++++++++++++++++++++--------
> fs/nfsd/vfs.c | 2 +-
> fs/overlayfs/overlayfs.h | 2 +-
> include/linux/fs.h | 3 +-
> include/uapi/linux/fcntl.h | 1 +
> 6 files changed, 150 insertions(+), 41 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 186bd2464fd5..2cc2b1deaa12 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4149,6 +4149,7 @@ SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newn
> * @dir: new parent
> * @new_dentry: where to create the new link
> * @delegated_inode: returns inode needing a delegation break
> + * @flags: link flags
> *
> * The caller must hold dir->i_mutex
> *
> @@ -4162,16 +4163,26 @@ SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newn
> * be appropriate for callers that expect the underlying filesystem not
> * to be NFS exported.
> */
> -int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode)
> +int vfs_link(struct dentry *old_dentry, struct inode *dir,
> + struct dentry *new_dentry, struct inode **delegated_inode,
> + unsigned int flags)
> {
> struct inode *inode = old_dentry->d_inode;
> + struct inode *target = new_dentry->d_inode;
> unsigned max_links = dir->i_sb->s_max_links;
> int error;
>
> if (!inode)
> return -ENOENT;
>
> - error = may_create(dir, new_dentry);
> + if (target) {
> + if (flags & AT_REPLACE)
This needs an
if (inode == target)
return 0;
I'll fix this in v4.
> + error = may_delete(dir, new_dentry, d_is_dir(old_dentry));
> + else
> + error = -EEXIST;
> + } else {
> + error = may_create(dir, new_dentry);
> + }
> if (error)
> return error;
>
next prev parent reply other threads:[~2018-04-24 22:14 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-24 6:19 [RFC PATCH v3 0/2] fs: add AT_REPLACE flag for linkat() Omar Sandoval
2018-04-24 6:19 ` [RFC PATCH v3 1/2] fs: add AT_REPLACE flag for linkat() which replaces the target Omar Sandoval
2018-04-24 22:14 ` Omar Sandoval [this message]
2018-04-24 6:19 ` [RFC PATCH v3 2/2] Btrfs: add support for linkat() AT_REPLACE Omar Sandoval
2018-04-24 13:21 ` [RFC PATCH v3 0/2] fs: add AT_REPLACE flag for linkat() Christoph Hellwig
2018-04-24 15:26 ` Omar Sandoval
2018-04-26 7:49 ` Omar Sandoval
2018-04-27 12:00 ` Michael Kerrisk (man-pages)
2018-05-04 18:29 ` Omar Sandoval
2018-05-04 18:30 ` Omar Sandoval
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