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I find a strange problem when I remount nfs in RHEL7.

I have shared 2 directories on nfs-server:

# showmount -e
Export list for localhost.localdomain:  
/file2 192.168.122.1  
/file1 192.168.122.1

Then I mount them on my client:

# sudo mount 192.168.122.100:/file2 /media  
# sudo mount 192.168.122.100:/file1 /mnt/file1
# mount 
192.168.122.100:/file1 on /mnt/file1 type nfs4 (rw,relatime,vers=4.0,rsize=131072,wsize=131072,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.122.1,local_lock=none,addr=192.168.122.100)
192.168.122.100:/file2 on /media type nfs4 (rw,relatime,vers=4.0,rsize=131072,wsize=131072,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.122.1,local_lock=none,addr=192.168.122.100)

Then I try remount one of them to ro:

# sudo mount -o ro,remount /mnt/file1/

That is the time strange thing happened, both of them changed to ro:

192.168.122.100:/file1 on /mnt/file1 type nfs4 (ro,relatime,vers=4.0,rsize=131072,wsize=131072,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.122.1,local_lock=none,addr=192.168.122.100)
192.168.122.100:/file2 on /media type nfs4 (ro,relatime,vers=4.0,rsize=131072,wsize=131072,namlen=255,hard,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.122.1,local_lock=none,addr=192.168.122.100)

I have captured some packets, but I find no packet sent when remount.

I just have no idea now, is there anyone can help me?

Thanks.

Barathrum
  • 79

1 Answers1

1

I find it.

It is because NFS use sharecache default. See in man nfs:

   sharecache / nosharecache
                  Determines  how  the  client's  data  cache and attribute cache are shared when mounting the same export more than once concurrently.  Using the same
                  cache reduces memory requirements on the client and presents identical file contents to applications when the same remote file is accessed  via  dif‐
                  ferent mount points.

                  If  neither  option  is  specified,  or  if the sharecache option is specified, then a single cache is used for all mount points that access the same
                  export.  If the nosharecache option is specified, then that mount point gets a unique cache.  Note that when data and attribute  caches  are  shared,
                  the mount options from the first mount point take effect for subsequent concurrent mounts of the same export.

                  As  of  kernel 2.6.18, the behavior specified by nosharecache is legacy caching behavior. This is considered a data risk since multiple cached copies
                  of the same file on the same client can become out of sync following a local update of one of the copies.

Man page says a single cache is used for all mount points that access the same export.

Then I use nosharecache option, it becomes normal now. 

192.168.122.100:/file1 on /mnt/file1 type nfs4 (ro,relatime,vers=4.0,rsize=131072,wsize=131072,namlen=255,hard,nosharecache,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.122.1,local_lock=none,addr=192.168.122.100)
192.168.122.100:/file2 on /mnt/file2 type nfs4 (rw,relatime,vers=4.0,rsize=131072,wsize=131072,namlen=255,hard,nosharecache,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.122.1,local_lock=none,addr=192.168.122.100
Barathrum
  • 79