Hi Amir, Jan Kara
Thanks for the responses so far. Appreciated.
I have taken step back, started afresh and performed another trial using the fanotify example program in another WSL2 setup.
1.) Uninstalled MDE software in WSL where FANOTIFY was initialized and that marks the mount point using mask: FAN_CLOSE_WRITE only. Ensured no pieces of monitoring software is present
2.) Ran the fanotify example program(without any changes) on p9 mount point and performed git clone on another session. Git clone was successful. This program was using mask FAN_OPEN_PERM and FAN_CLOSE_WRITE.
3.) Modified the fanotify example program to mark the mount point using mask FAN_CLOSE_WRITE only. Ran the git clone. The operation fails.
Is it something to do with mask ?
I didn't get a chance to run on standard linux kernel. Can you share the commands to do so of mounting 9p on standard linux
Thank you,
Krishna Vivek
-----Original Message-----
From: Amir Goldstein <amir73il@xxxxxxxxx>
Sent: Wednesday, September 25, 2024 5:26 PM
To: Jan Kara <jack@xxxxxxx>
Cc: Krishna Vivek Vitta <kvitta@xxxxxxxxxxxxx>; linux-fsdevel@xxxxxxxxxxxxxxx; Eric Van Hensbergen <ericvh@xxxxxxxxxx>; Latchesar Ionkov <lucho@xxxxxxxxxx>; Dominique Martinet <asmadeus@xxxxxxxxxxxxx>; v9fs@xxxxxxxxxxxxxxx
Subject: Re: [EXTERNAL] Re: Git clone fails in p9 file system marked with FANOTIFY
On Wed, Sep 25, 2024 at 1:38 PM Jan Kara <jack@xxxxxxx> wrote:
>
> [Adding 9p guys to CC]
>
> On Wed 25-09-24 12:51:38, Amir Goldstein wrote:
> > On Wed, Sep 25, 2024 at 10:18 AM Jan Kara <jack@xxxxxxx> wrote:
> > > On Wed 25-09-24 10:11:46, Jan Kara wrote:
> > > > On Tue 24-09-24 12:07:51, Krishna Vivek Vitta wrote:
> > > > > Please ignore the last line.
> > > > > Git clone operation is failing with fanotify example code as well.
> > > > >
> > > > > root@MININT-S244RA7:/mnt/c/Users/kvitta/Desktop/MDE
> > > > > binaries/GitCloneIssue# ./fanotify_ex /mnt/c Press enter key to terminate.
> > > > > root@MININT-S244RA7:/mnt/c/Users/kvitta/Desktop/MDE
> > > > > binaries/GitCloneIssue# ./fanotify_ex /mnt/c Press enter key to terminate.
> > > > > Listening for events.
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/info/exclude
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/info/exclude
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-applypatch.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-applypatch.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/applypatch-msg.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/applypatch-msg.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/commit-msg.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/commit-msg.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-push.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-push.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-merge-commit.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-merge-commit.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-commit.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-commit.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/post-update.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/post-update.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/push-to-checkout.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/push-to-checkout.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/fsmonitor-watchman.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/fsmonitor-watchman.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/update.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/update.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-rebase.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-rebase.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-receive.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/pre-receive.sample
> > > > > FAN_OPEN_PERM: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/prepare-commit-msg.sample
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/hooks/prepare-commit-msg.sample
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/description
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/description
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/HEAD.lock
> > > > > FAN_CLOSE_WRITE: File /mnt/c/Users/kvitta/gtest/.git/HEAD.lock
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config.lock
> > > > > FAN_CLOSE_WRITE: File
> > > > > /mnt/c/Users/kvitta/gtest/.git/config.lock
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config.lock
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_CLOSE_WRITE: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config.lock
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_CLOSE_WRITE: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config.lock
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_CLOSE_WRITE: File /mnt/c/Users/kvitta/gtest/.git/config
> > > > > FAN_OPEN_PERM: File /mnt/c/Users/kvitta/gtest/.git/tNbqjiA
> > > > > read: No such file or directory
> > > > > root@MININT-S244RA7:/mnt/c/Users/kvitta/Desktop/MDE
> > > > > binaries/GitCloneIssue#
> > > >
> > > > OK, so it appears that dentry_open() is failing with ENOENT when
> > > > we try to open the file descriptor to return with the event.
> > > > This is indeed unexpected from the filesystem.
> >
> > How did you conclude that is what is happening?
> > Were you able to reproduce, because I did not.
>
> No, I didn't reproduce. But checking the source of the reproducer the
> message "read: No such file or directory" means fanotify_read() has
> returned -ENOENT and within fanotify there's no way how that could happen.
> So the only possible explanation is that dentry_open() returns it.
>
Ah, I missed that bit in the report.
> > > > On the other hand we already do silently fixup similar
> > > > EOPENSTALE error that can come from NFS so perhaps we should be
> > > > fixing ENOENT similarly? What do you thing Amir?
> > >
> >
> > But we never return this error to the caller for a non-permission
> > event, so what am I missing?
>
> Umm. If dentry_open() fails, we return the error from
> copy_event_to_user() without copying anything. Then fanotify_read() does:
>
> ret = copy_event_to_user(group, event, buf, count);
> ...
> if (!fanotify_is_perm_event(event->mask)) {
> fsnotify_destroy_event(group, &event->fse);
> // unused event destroyed
> } else {
> ...
> }
> if (ret < 0)
> break; // read loop aborted
> ...
> }
> ...
> if (start != buf && ret != -EFAULT)
> ret = buf - start;
> return ret;
>
> So the error *is* IMO returned to userspace if this was the first event.
>
Yes it is "returned to userspace" but it is returned to the fanotify listener.
The original complaint is about the error returned to open(2) after rename(2) in the rename_try.c reproducer (when fanotify is watching close events).
I admit that fanotify_read() randomly returning an error is sub-optimal, but I do prefer it over dropping the error silently.
BTW, there are several other dentry_open() errors that are easy to reproduce in this context:
ENXIO after an event on a pipe with no reader ENODEV after an event on a device node with no backing instance
These were part of the reason that I excluded special files from new pre-content events...
Thanks,
Amir.
