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From:   Gefei Li <gefeili.2013@gmail.com>
Date:   Mon, 18 Feb 2019 17:11:47 +0800
Message-ID: <CANidX5RGLuvdS82TpxuagUsA4DmUochDv2AwX7rwHdD-q+Khbg@mail.gmail.com>
Subject: linux NFS client lock file cannot get a expected response
To:     linux-nfs@vger.kernel.org
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Sender: linux-nfs-owner@vger.kernel.org
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Hi NFSDevs,

I am recently testing linux nfs lock with NFS share from a WinServer
2016. I tried to write a file which has already been locked with fcntl
exclusively, but the response of `write` syscall is neither
`Permission denied`, nor successfully written with file content
changed. Here is several experiments I did:

The first shell runs c program, calling `fcntl` to lock file
exclusively =E2=80=9Cfcntl(fd, F_SETLKW, &fl)=E2=80=9D

2.1 The second shell tried to open with flag O_RDWR, and write a
buffer to the same file, write returned the correct bytes written, but
the file content remained unchanged.
2.2 The second shell tried to open with flag O_RDWR|O_SYNC, write the
same buffer to the same file, write operation returned EAGAIN
2.3 The same operation on ext4 file system gives me a expected
behavior the same as advisory lock expressed, successfully written
with file content changed.

I reviewed NFS 4.1 protocol(RFC 5661 page 185), the nfs server can
determine whether byte range lock can be either mandatory or advisory,
but I think 2.1 and 2.2 gives me some unexpected behavior as these
two.. What=E2=80=99s your idea about this? Can you give me some tips to wor=
k
this out?

Looking forward for your reply. Thanks in advance!

BTW, my linux kernel version is 4.15.0, linux release: ubuntu 16.04
from Azure marketplace, my nfs-common version is
"nfs-common/xenial-updates,now 1:1.2.8-9ubuntu12.1 amd64" from ubuntu
apt repo.

Thanks,
Gefei