On Tue, Jan 2, 2018 at 6:51 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> On Tue, Jan 02, 2018 at 02:26:48PM +0200, Amir Goldstein wrote:
>> Currently with overlayfs, the real upper inode's i_mtime is updated on
>> write, but not overlay vfs inode. The vfs inode's i_mtime is used by nfsd
>> to check if nfs client cache is stale, so updating the overlay vfs inode
>> i_mtime on write is required for overlayfs NFS export support.
>>
>> The non uptodate mtime issue was found and verified with the
>> nfstest_posix test when run over NFS exported overlayfs:
>>
>> $ nfstest_posix --runtest=write
>> ...
>> FAIL: write - file st_mtime should be updated
>>
>> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
>> ---
>> fs/inode.c | 9 ++++++---
>> 1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/inode.c b/fs/inode.c
>> index 03102d6ef044..a252256f4e51 100644
>> --- a/fs/inode.c
>> +++ b/fs/inode.c
>> @@ -1567,8 +1567,7 @@ EXPORT_SYMBOL(bmap);
>> /*
>> * Update times in overlayed inode from underlying real inode
>> */
>> -static void update_ovl_inode_times(struct dentry *dentry, struct inode *inode,
>> - bool rcu)
>> +static void update_ovl_d_inode_times(struct dentry *dentry, bool rcu)
>> {
>> struct dentry *upperdentry;
>>
>> @@ -1585,6 +1584,7 @@ static void update_ovl_inode_times(struct dentry *dentry, struct inode *inode,
>> * stale mtime/ctime.
>> */
>> if (upperdentry) {
>> + struct inode *inode = d_inode(dentry);
>> struct inode *realinode = d_inode(upperdentry);
>>
>> if ((!timespec_equal(&inode->i_mtime, &realinode->i_mtime) ||
>> @@ -1607,7 +1607,8 @@ static int relatime_need_update(const struct path *path, struct inode *inode,
>> if (!(path->mnt->mnt_flags & MNT_RELATIME))
>> return 1;
>>
>> - update_ovl_inode_times(path->dentry, inode, rcu);
>> + update_ovl_d_inode_times(path->dentry, rcu);
>> +
>
> Hi Amir,
>
> If we update overlay inode mtime, ctime in write path, then do we still
> need this call in relatime_need_update() path? I mean what other path
> is there where real inode mtime/ctime will be out of sync with overlay
> inode mtime/ctime.
>
Specifically, in the mentioned nfstest_posix test, i_mtime was not
updated on write of regular file and i_mtime of parent was not updated on link.
I guess there are more cases where i_mtime is updated not in the
write() path. I can think of punch hole for regular files and even file system
specific ioctls, which overlayfs is not aware of.
To handle those cases, I added the 2nd patch, which is "mtime reader
oriented", just like the relatime_need_update() case.
The problem is that AFAIK there is no simple place where all
i_mtime updates can be intercepted. Perhaps the recent work by Jeff
to sort out i_version readers/writers will provide a better place
to intercept all mtime updates?? At least for underlying filesystems that
support i_version, we could update overlay inode times only if i_version
was updated, but I don't even know what would be the best implementation
choice for relatime_need_update() in that case.
Amir.
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