Thanks a lot for the '/proc/fs/cifs/Stats | grep "Open files"' tip,
Steve. But it seems not working in my case(not crashing case).
I have an SMB server that is able to close handles from server side,
and if closed remotely I want to check from client side. I've done
several experiments:
1. CIFS client open, server side close
- both "/proc/fs/cifs/Stats" and "cat /proc/fs/cifs/open_files"
remain unchanged
2. CIFS client open, server side close, client side call "close"
function to check fd
- "Closes" in "/proc/fs/cifs/Stats" changes "4 total 1 failed" <-
1 failed due to server side closed?
3. CIFS client open, server side close, client side call "read"
function to check fd
- EBADF returned while trying to "read", this is what I expect. But
for dir handle and WR-only handles, which function should I use?
Regards,
Gefei
On Sun, Jul 28, 2019 at 8:08 AM Steve French <smfrench@xxxxxxxxx> wrote:
>
> On Fri, Jul 26, 2019 at 3:22 AM Gefei Li <gefeili.2013@xxxxxxxxx> wrote:
> >
> > Hi,
> >
> > From some stack overflow result I know that on a local ext4/fat32
> > system, we can test whether a file descriptor is valid through
> > "fcntl(fd, F_GETFD)". But in cifs cases, a fd typically bind a local
> > fd to remote handle, do we have some c function/syscall that can test
> > whether the fd is remotely closed?
> >
> > I've tried some windows way like "ioctl", which works well, and in
> > linux local file system "fcntl" works. Tried to use "fcntl" on kernel
> > 5.1.15, found no server request is received.. Could you please give me
> > some advice on testing whether a fd is remoted closed in CIFS client?
>
> both F_GETFD and F_GETFL look like they check in the local VFS only
> (aren't passed down to the file system, whether ext4 or cifs or even nfs)
> for the value of these flags (see do_fcntl function in fs/fcntl.c)
>
> In general an open of a file (over an SMB3 mount) will result in a open
> over a file on the server. You can see the detailed information on
> the network file handle ("PersistentFileID") open on the server by (on
> the Linux client) doing:
>
> cat /proc/fs/cifs/open_files
>
> If you were worried about a network crash temporarily closing remote handles
> (in which case you might temporarily have a local handle which is not
> open on the
> server) you could (in theory) do:
>
> /proc/fs/cifs/Stats | grep "Open files"
>
> but I did notice a bug (in the processing of one of those counters for
> that /proc file)
> in which we are leaking one of those two counters (the counter is
> informational only
> so presumably not a serious bug) and it can go negative so looking at the count
> of open files on the server may not be as useful.
>
> --
> Thanks,
>
> Steve
