On Mon, Dec 18, 2017 at 2:55 PM, Chengguang Xu <cgxu519@xxxxxxxxxx> wrote:
> Inspired by encountering unexpected write error when
> upperdir and workdir having different project ids.
> So if upper filesystem supports O_TMPFILE, try to check
> link ability between upperdir and workdir and print a
> warning message if check fails.
> The failure of check does not directly lead to read-only
> mounting because in some use cases may only write to
> upperdir and do not modify anything on lowerdirs.
>
> Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxx>
> ---
Looks good.
Amir.
>
> Changes since v2:
> - Add comment about motivation.
> - Modify warning message.
>
> Changes since v1:
> - Check link ablity between upperdir and workdir instead of checking
> project ids of upperdir and workdir.
> - Print a warning message instead of falling to readonly mode.
>
> fs/overlayfs/super.c | 30 +++++++++++++++++++++++-------
> 1 file changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 76440fe..7d6bd82 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -929,7 +929,7 @@ static int ovl_get_upper(struct ovl_fs *ofs, struct path *upperpath)
>
> static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
> {
> - struct dentry *temp;
> + struct dentry *uppertemp, *worktemp;
> int err;
>
> ofs->workdir = ovl_workdir_create(ofs, OVL_WORKDIR_NAME, false);
> @@ -953,12 +953,28 @@ static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
> if (!err)
> pr_warn("overlayfs: upper fs needs to support d_type.\n");
>
> - /* Check if upper/work fs supports O_TMPFILE */
> - temp = ovl_do_tmpfile(ofs->workdir, S_IFREG | 0);
> - ofs->tmpfile = !IS_ERR(temp);
> - if (ofs->tmpfile)
> - dput(temp);
> - else
> + /*
> + * Check if upper/work fs supports O_TMPFILE and if support, check
> + * link ability between upperdir and workdir, this is inspired by
> + * encountering unexpected write error when upperdir and workdir
> + * having different project ids.
> + */
> + uppertemp = ovl_do_tmpfile(ofs->upper_mnt->mnt_root, S_IFREG | 0);
> + ofs->tmpfile = !IS_ERR(uppertemp);
> + if (ofs->tmpfile) {
> + worktemp = ovl_lookup_temp(ofs->workdir);
> + if (!IS_ERR(worktemp)) {
> + inode_lock_nested(ofs->workdir->d_inode, I_MUTEX_PARENT);
> + err = ovl_do_link(uppertemp, ofs->workdir->d_inode, worktemp, true);
> + inode_unlock(ofs->workdir->d_inode);
> + if (err)
> + pr_warn("overlayfs: cannot link files between upperdir and workdir, it may cause write error.\n");
> + else
> + ovl_cleanup(ofs->workdir->d_inode, worktemp);
> + dput(worktemp);
> + }
> + dput(uppertemp);
> + } else
> pr_warn("overlayfs: upper fs does not support tmpfile.\n");
>
> /*
> --
> 1.8.3.1
>
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