From: Wei Yongjun <yjwei@cn.fujitsu.com>
Subject: Re: Question: When NFS client check dir's permission,
 it does not check the cache data
Date: Thu, 28 Jun 2007 11:06:14 +0800
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To: Trond Myklebust <trond.myklebust@fys.uio.no>
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>> I mean that read a dir, such as lookup a dir.
>> If I reply a getattr as that dir has no lookup permission, and then do a
>> "cat /nfsroot/dir/file" at client, client will not send lookup procedure to
>> server, because client used the cache data of the dir. It like this:
>> client server
>> #ls /nfsroot
>> readdirplus ------------------>
>> <------------- readdirplus reply
>> (attribute of dir has no lookup permission)
>> # cat /nfsroot/dir/file
>> (send nothing, used cache data)
>> -------no package is send-------
>>
>> If no cache data exists, it would like this:
>> client server
>> #ls /nfsroot
>> readdirplus ------------------>
>> <------------- readdirplus reply
>> (attribute of dir has no lookup permission)
>> # cat /nfsroot/dir/file
>> access(dir) ------------------->
>> <------------- access reply(dir)
>> (has no lookup permission)
>>
>> And if has permission to lookup dir, it would like this:
>> client server
>> #ls /nfsroot
>> readdirplus ------------------>
>> <------------- readdirplus reply
>> (attribute of dir has no lookup permission)
>> # cat /nfsroot/dir/file
>> access(dir) -------------------> (*1)
>> <------------- access reply(dir)
>> lookup(file) ------------------->
>> <------------- lookup reply(file)
>> read(file) ------------------->
>> <------------- read reply(file)
>>
>> While you optimize all write operations to omit access procedure, can
>> this access (*1) be omitted? Then lookup(file) will return NOPERM.
>>     
>
> So what if I change the permissions on the directory? What should the
> rules be for caching these attributes?
>
> ...and you still haven't replied to my question about what
> application/workload actually _cares_ about optimising for this
> particular case.
>   
No application cares this ^_^, just for test.
I test the read op of dir, it maybe has tiny bug in it. As you said, if
I chmod of dir, client will be a little later to know this.
Test step ad following:

[root@REHL ~]# mount -t nfs 192.168.0.19:/nfsroot /mnt
[root@REHL ~]# ll /mnt
total 4
dr-xr-xr-x 2 root root 4096 Jun 23  2007 dir
[root@REHL ~]# ll /mnt/dir
total 4
-rw-r--r-- 1 root root 5 Jun 24  2007 file
[root@REHL ~]# su weiyj
[weiyj@REHL root]$ ll /mnt
total 4
dr-xr-xr-x 2 root root 4096 Jun 23  2007 dir
[weiyj@REHL root]$ ll /mnt/dir
total 4
-rw-r--r-- 1 root root 5 Jun 24  2007 file
[weiyj@REHL root]$ cat /mnt/dir/file
test
[weiyj@REHL root]$ ssh 192.168.0.19 -l root chmod a-x /nfsroot/dir
[weiyj@REHL root]$ cat /mnt/dir/file
test
[weiyj@REHL root]$ cat /mnt/dir/file
test
[weiyj@REHL root]$ ll /mnt/dir
total 0
?--------- ? ? ? ?            ? /mnt/dir/file
[weiyj@REHL root]$ ll /mnt
total 4
dr--r--r-- 2 root root 4096 Jun 23  2007 dir
[weiyj@REHL root]$ cat /mnt/dir/file
cat: /mnt/dir/file: Permission denied


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