On 07/27/2011 11:03 PM, Christoph Hellwig wrote:
On Wed, Jul 27, 2011 at 01:02:59PM +0200, Bernd Schubert wrote:
Use 32-bit or 64-bit llseek() hashes for directory offsets depending on
the NFS version. NFSv2 gets 32-bit hashes only.
Independent of the O_ vs FMODE thing make sure you pass the correct
flag at open time, instead of racy runtime modifications.
Christoph,
before I'm going to work further on the patch sets, I have few questions
first. Could you please help me with that?
file->f_mode is set in __dentry_open() based on O_ flags.
So if f_mode is supposed to be set directly during the NFS open call we
would need O_ *and* FMODE flags,
Now I still do not understand why we cannot add a flag *after* the open
call and only in nfsd_readdir()? I do not see any races there.
nfsd_readdir() gets its 'struct file' from get_empty_filp() and
__dentry_open(). Now as 'struct file' is allocated by get_empty_filp()
it also cannot be used by any other thread.
nfsd_readdir() just reads the directory and closes it immedeatily after
the readdir().
So where is there supposed to be a race?
And lastly, if we are going to set f_mode directly at open time, we have
the choice to
1) Specify those new O_ flags for all files. While setting a flag is a
cheap operation, it still wastes CPU cycles for file opens, as files do
not need that flag.
2) Duplicate nfsd_open() to implement a new function for directories
only. I think not a good idea either.
3) Rewrite the nfsd_open() function to allow to set flags from calling
functions. That would mean to update the nfsd code at at least 8 places.
Do we really want to go that way?
So altogether, updating the patches to replace O_ by FMODE flags is
easy, but setting that flag in nfsd at open time, would mean a large
overhead.
Thanks,
Bernd
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