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: Wed, 27 Jun 2007 13:22:03 +0800
Message-ID: <4681F3FB.7040609@cn.fujitsu.com>
References: <467F8247.9060607@cn.fujitsu.com>	
	<1182802099.6163.33.camel@heimdal.trondhjem.org>	
	<4681BC44.6000605@cn.fujitsu.com>
	<1182913754.12836.61.camel@heimdal.trondhjem.org>
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To: Trond Myklebust <trond.myklebust@fys.uio.no>
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>
>> I think code "status = nfs_access_get_cached(inode, cred, &cache);" can do
>> this. And it works.
>> Other question: why only optimize all write operations, read operations
>> are not optimized? If read options is optimized, it can do the same things,
>> do not use access to check permissions, and server will check permissions
>> when we perform the read op.
>>     
>
> Huh? What read operations are we failing to optimise and how?
>   

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.

Regards
Wei Yongjun


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