On Mon, Jun 1, 2020 at 5:04 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Sat, May 30, 2020 at 01:37:37PM +0300, Amir Goldstein wrote: > > On Sat, May 30, 2020 at 12:30 AM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > > > > > overlayfs can keep index of copied up files and directories and it > > > seems to serve two primary puroposes. For regular files, it avoids > > > breaking lower hardlinks over copy up. For directories it seems to > > > be used for various error checks. > > > > > > During ovl_lookup(), we lookup for index using lower dentry in many > > > a cases. That lower dentry is called "origin" and following is a summary > > > of current logic. > > > > > > If there is no upperdentry, always lookup for index using lower dentry. > > > For regular files it helps avoiding breaking hard links over copyup > > > and for directories it seems to be just error checks. > > > > > > If there is an upperdentry, then there are 3 possible cases. > > > > > > - For directories, lower dentry is found using two ways. One is regular > > > path based lookup in lower layers and second is using ORIGIN xattr > > > on upper dentry. First verify that path based lookup lower dentry > > > matches the one pointed by upper ORIGIN xattr. If yes, use this > > > verified origin for index lookup. > > > > > > - For regular files (non-metacopy), there is no path based lookup in > > > lower layers as lookup stops once we find upper dentry. So there > > > is no origin verification. If there is ORIGIN xattr present on upper, > > > use that to lookup index otherwise don't. > > > > > > - For regular metacopy files, again lower dentry is found using > > > path based lookup as well as ORIGIN xattr on upper. Path based lookup > > > is continued in this case to find lower data dentry for metacopy > > > upper. So like directories we only use verified origin. If ORIGIN > > > xattr is not present (Either because lower did not support file > > > handles or because this is hardlink copied up with index=off), then > > > don't use path lookup based lower dentry as origin. This is same > > > as regular non-metacopy file case. > > > > > > > Very good summary. > > You may add: > > Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx> > > > > But see one improvement below. > > Also, please make sure to run unionmount setups: > > > > ./run --ov=10 --verify > > ./run --ov=10 --meta --verify > > > > --verify will enable index and check st_dev;st_ino are not broken > > on copy up. --ov=10 will cause lower hardlink copy up, because > > after hardlink is creates by some test, upper is rotated to mid layer > > and next modifying operation will trigger the hardlink copy up. > > Hi Amir, > > I ran above configurations and it passes with the patches. > > Thanks for these suggestions. I used to run only "./run --ov" so far. > It will be nice to have some documentation about --meta, --verify in README. > Yeh, I never get to it. But now I finally posted xfstest integration, so we can just add more xfstests to run metacopy configurations on a full test cycle. > > > > > Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx> > > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> > > > --- > > > fs/overlayfs/namei.c | 29 +++++++++++++++++------------ > > > 1 file changed, 17 insertions(+), 12 deletions(-) > > > > > > diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c > > > index 0db23baf98e7..5d80d8cc0063 100644 > > > --- a/fs/overlayfs/namei.c > > > +++ b/fs/overlayfs/namei.c > > > @@ -1005,25 +1005,30 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, > > > } > > > stack = origin_path; > > > ctr = 1; > > > + origin = origin_path->dentry; > > > origin_path = NULL; > > > } > > > > > [...] > > > - if (ctr && (!upperdentry || (!d.is_dir && !metacopy))) > > > + if (!origin && ctr && !upperdentry) > > > origin = stack[0].dentry; > > > > > > > No need to understand the long story to verify this change is correct. > > This is true simply because the conditions to set stack = origin_path are: > > > > if (!metacopy && !d.is_dir && upperdentry && !ctr && origin_path) > > > > And after getting there and setting ctr = 1, the complex conditions to > > setting origin are met for certain: > > > > if (ctr && (!upperdentry || (!d.is_dir && !metacopy))) > > > > Therefore, it is logically equivalent (and makes much more sense) > > to assign origin near stack = origin_path. > > > > Further, thanks to Vivek's explanation, it is now clear to me that after > > setting origin above, all that is left to do here is: > > > > /* Always lookup index of non-upper */ > > if (!upperdentry) > > origin = stack[0].dentry; > > This looks better. What about the case of non existing dentry with ctr=0. > In that case we will set origin to NULL. It still works but it probably > will be nice if we do. Forgot about that. > > /* Always lookup index of non-upper */ > if (!upperdentry && ctr) > origin = stack[0].dentry; > > Just making it explicit that we try to use lower as origin only if > some lower dentry was found. > Looks good. Sustaining my RVB Thanks, Amir.
