On Wed, Feb 27, 2019 at 1:32 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> Overlay file f_pos is the master copy that is preserved
> through copy up and modified on read/write, but only real
> fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
> limitations that are more strict than ->s_maxbytes for specific
> files, so we use the real file to perform seeks.
>
> We do not call real fs for SEEK_CUR:0 query and for SEEK_SET:0
> requests.
>
> Fixes: d1d04ef8572b ("ovl: stack file ops")
> Reported-by: Eddie Horng <eddiehorng.tw@xxxxxxxxx>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
Miklos,
PING.
xfstests are already upstream and failing...
Thanks,
Amir.
>
> Changes since v1:
> - Take ovl inode lock
> - Optimize SEEK_CUR:0 and SEEK_SET:0 cases
>
> fs/overlayfs/file.c | 44 ++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 40 insertions(+), 4 deletions(-)
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 84dd957efa24..db7bd3319b35 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -145,11 +145,47 @@ static int ovl_release(struct inode *inode, struct file *file)
>
> static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
> {
> - struct inode *realinode = ovl_inode_real(file_inode(file));
> + struct inode *inode = file_inode(file);
> + struct fd real;
> + const struct cred *old_cred;
> + ssize_t ret;
> +
> + /*
> + * The two special cases below do not need to involve real fs,
> + * so we can optimizing concurrent callers.
> + */
> + if (offset == 0) {
> + if (whence == SEEK_CUR)
> + return file->f_pos;
> +
> + if (whence == SEEK_SET)
> + return vfs_setpos(file, 0, 0);
> + }
> +
> + ret = ovl_real_fdget(file, &real);
> + if (ret)
> + return ret;
>
> - return generic_file_llseek_size(file, offset, whence,
> - realinode->i_sb->s_maxbytes,
> - i_size_read(realinode));
> + /*
> + * Overlay file f_pos is the master copy that is preserved
> + * through copy up and modified on read/write, but only real
> + * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
> + * limitations that are more strict than ->s_maxbytes for specific
> + * files, so we use the real file to perform seeks.
> + */
> + inode_lock(inode);
> + real.file->f_pos = file->f_pos;
> +
> + old_cred = ovl_override_creds(inode->i_sb);
> + ret = vfs_llseek(real.file, offset, whence);
> + revert_creds(old_cred);
> +
> + file->f_pos = real.file->f_pos;
> + inode_unlock(inode);
> +
> + fdput(real);
> +
> + return ret;
> }
>
> static void ovl_file_accessed(struct file *file)
> --
> 2.17.1
>
