On Wed, Jan 08, 2014 at 11:10:09PM +0100, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> If this flag is specified and the target of the rename exists then the
> rename syscall fails with EEXIST.
Why is this useful?
(I'm sure it is, it'd just be useful to have the reasons recorded
someplace.)
> 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.
Till that's done this should probably result in -EOPNOTSUPP on those
filesystems?
I think this would need new protocol in the NFS case.
--b.
>
> Suggested-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> ---
> fs/ext4/namei.c | 2 +-
> fs/namei.c | 21 +++++++++++++--------
> include/uapi/linux/fs.h | 2 ++
> 3 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 08c40f4e7eed..e0129b6e74cf 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -3021,7 +3021,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
> int inlined = 0, new_inlined = 0;
> struct ext4_dir_entry_2 *parent_de;
>
> - if (flags)
> + if (flags & ~RENAME_NOREPLACE)
> return -EOPNOTSUPP;
>
> dquot_initialize(old_dir);
> diff --git a/fs/namei.c b/fs/namei.c
> index 593673fcbfef..f9cf3020394c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4123,7 +4123,7 @@ SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
> bool should_retry = false;
> int error;
>
> - if (flags)
> + if (flags & ~RENAME_NOREPLACE)
> return -EOPNOTSUPP;
>
> retry:
> @@ -4149,6 +4149,8 @@ retry:
> goto exit2;
>
> new_dir = newnd.path.dentry;
> + if (flags & RENAME_NOREPLACE)
> + error = -EEXIST;
> if (newnd.last_type != LAST_NORM)
> goto exit2;
>
> @@ -4171,22 +4173,25 @@ 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)
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 6c28b61bb690..9250f4dd7d96 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -35,6 +35,8 @@
> #define SEEK_HOLE 4 /* seek to the next hole */
> #define SEEK_MAX SEEK_HOLE
>
> +#define RENAME_NOREPLACE (1 << 0) /* Don't overwrite target */
> +
> struct fstrim_range {
> __u64 start;
> __u64 len;
> --
> 1.8.1.4
>
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