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authorMiklos Szeredi <mszeredi@suse.cz>2014-04-01 17:08:43 +0200
committerMiklos Szeredi <mszeredi@suse.cz>2014-04-01 17:08:43 +0200
commit0a7c3937a1f23f8cb5fc77ae01661e9968a51d0c (patch)
tree8924086bfd279409f9eb83aab9a6177e0748b257 /fs/namei.c
parent520c8b16505236fc82daa352e6c5e73cd9870cff (diff)
downloadop-kernel-dev-0a7c3937a1f23f8cb5fc77ae01661e9968a51d0c.zip
op-kernel-dev-0a7c3937a1f23f8cb5fc77ae01661e9968a51d0c.tar.gz
vfs: add RENAME_NOREPLACE flag
If this flag is specified and the target of the rename exists then the rename syscall fails with EEXIST. The VFS does the existence checking, so it is trivial to enable for most local filesystems. This patch only enables it in ext4. For network filesystems the VFS check is not enough as there may be a race between a remote create and the rename, so these filesystems need to handle this flag in their ->rename() implementations to ensure atomicity. Andy writes about why this is useful: "The trivial answer: to eliminate the race condition from 'mv -i'. Another answer: there's a common pattern to atomically create a file with contents: open a temporary file, write to it, optionally fsync it, close it, then link(2) it to the final name, then unlink the temporary file. The reason to use link(2) is because it won't silently clobber the destination. This is annoying: - It requires an extra system call that shouldn't be necessary. - It doesn't work on (IMO sensible) filesystems that don't support hard links (e.g. vfat). - It's not atomic -- there's an intermediate state where both files exist. - It's ugly. The new rename flag will make this totally sensible. To be fair, on new enough kernels, you can also use O_TMPFILE and linkat to achieve the same thing even more cleanly." Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Reviewed-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'fs/namei.c')
-rw-r--r--fs/namei.c21
1 files changed, 13 insertions, 8 deletions
diff --git a/fs/namei.c b/fs/namei.c
index ab4e48c..0e9d186 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4142,7 +4142,7 @@ SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
bool should_retry = false;
int error;
- if (flags)
+ if (flags & ~RENAME_NOREPLACE)
return -EINVAL;
retry:
@@ -4168,6 +4168,8 @@ retry:
goto exit2;
new_dir = newnd.path.dentry;
+ if (flags & RENAME_NOREPLACE)
+ error = -EEXIST;
if (newnd.last_type != LAST_NORM)
goto exit2;
@@ -4190,22 +4192,25 @@ retry_deleg:
error = -ENOENT;
if (d_is_negative(old_dentry))
goto exit4;
+ new_dentry = lookup_hash(&newnd);
+ error = PTR_ERR(new_dentry);
+ if (IS_ERR(new_dentry))
+ goto exit4;
+ error = -EEXIST;
+ if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
+ goto exit5;
/* unless the source is a directory trailing slashes give -ENOTDIR */
if (!d_is_dir(old_dentry)) {
error = -ENOTDIR;
if (oldnd.last.name[oldnd.last.len])
- goto exit4;
+ goto exit5;
if (newnd.last.name[newnd.last.len])
- goto exit4;
+ goto exit5;
}
/* source should not be ancestor of target */
error = -EINVAL;
if (old_dentry == trap)
- goto exit4;
- new_dentry = lookup_hash(&newnd);
- error = PTR_ERR(new_dentry);
- if (IS_ERR(new_dentry))
- goto exit4;
+ goto exit5;
/* target should not be an ancestor of source */
error = -ENOTEMPTY;
if (new_dentry == trap)
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