On 12/15/2011 02:58 PM, Myklebust, Trond wrote:
-----Original Message-----
From: Maxim Uvarov [mailto:maxim.uvarov@xxxxxxxxxx]
Sent: Thursday, December 15, 2011 5:34 PM
To: Myklebust, Trond
Cc: Al Viro; linux-nfs@xxxxxxxxxxxxxxx; bfields@xxxxxxxxxxxx;
john@xxxxxxxxxxxxxxxxx; rlove@xxxxxxxxx; eparis@xxxxxxxxxxxxxx
Subject: Re: [PATCH] NFS/INOTIFY: inotify user when deleting files on
nfs
On 12/15/2011 01:52 PM, Myklebust, Trond wrote:
-----Original Message-----
From: Al Viro [mailto:viro@xxxxxxxxxxxxxxxxxx]
Sent: Thursday, December 15, 2011 4:33 PM
To: Maxim Uvarov
Cc: linux-nfs@xxxxxxxxxxxxxxx; bfields@xxxxxxxxxxxx; Myklebust,
Trond; john@xxxxxxxxxxxxxxxxx; rlove@xxxxxxxxx;
eparis@xxxxxxxxxxxxxx
Subject: Re: [PATCH] NFS/INOTIFY: inotify user when deleting files
on
nfs
On Thu, Dec 15, 2011 at 11:12:30AM -0800, Maxim Uvarov wrote:
1. Original VFS code already has "if NFS", in vfs_unlink().
Because
of
code does not call d_delete() it has to call notification from
d_delete().
2. inotify is done on VFS layer. So logically it has to work on
all
file systems.
You are using a very odd meaning of the word "logically", then.
Note
that
inotify does *not* work on NFS, no matter what vfs_unlink() would
do.
Simply because files are removed on server, not in VFS. And server
does not
notify clients of such removals. Ergo, any software that relies on
inotify
delivering notifications of files being removed is broken on NFS.
That has nothing whatsoever to the layer in kernel where it's
handled;
the
information asked for is simply not available to client. Period.
Incidentally, inotify does not work on a bunch of local
filesystems,
starting
with procfs. And won't work, unless you are seriously proposing to
generate
events on things like open()/dup2()/etc. In this case we might
very
well have
objects appearing and disappearing without ever having had a
dentry.
The other thing to note is that even if there were value in having
only client support for the locally performed operations, the way
NFS
deletes work is fundamentally different to the way that POSIX unlink
works: if the file is still open, it isn't deleted, it is just
renamed. In consequence, it not only still appears in readdir()
requests (albeit under a different name), but it acts in all ways
shapes and forms as the same regular file but with the curious
property that when the last user closes it gets deleted.
IOW: the assumption that we would need to generate an
fsnotify_nameremove event here is in any case flawed. It would
rather
be fsnotify_move, which I suspect would still trip up these LTP
tests...
Cheers
Trond
Thanks. My original idea was to generate absolutely the same event
under
unlink(). Yes, original file in that case is not deleted, it is moved.
But from user side it's deletion. Users don't take care about
/tmp/.nfs.. files,
right? When you call unlink the only thing you do is to check return
code, you
are not walking along all folders to check where it could be moved.
It is not deletion because it is not an atomic operation.
Until the last close occurs. ls -a will still list the .nfsxxxx entry.
Most operations that the user may expect to fail on a deleted file such
as link(), open(), access(), stat(), etc. will still succeed provided
that you use the .nfsxxxx name. On the other hand, an operation such as
rmdir() on the parent directory will not succeed because it still
contains at least one file entry...
I also agree that if server or other mounts does something with file,
server
will not send any notification. But for single mount it has to be ok.
What's the killer application?
No application, I only have information that one of LTP tests is failed.
Maxim.
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