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>
---
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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