Re: Reg file system hash function

[Russell King]

On Fri, Jun 15, 2001 at 03:52:52PM +0530, SATHISH.J wrote:
> In the vfs layer when we see the lookup_dentry() function code we see that
> a part of the code checks whether low level filesystem wants to use its
> own hash. the part odf the code that calls the filesystem dependant
> hashing is  "error = base->d_op->d_hash->(base,&this);". Why should it
> callfilesystem dependant hashing. What is the main purpose of hashing
> here.
> Please help me with these details. 

It is used in two cases.  If a filesystem has:

1. case-insensitive filenames (its much better to have the names 'FOO' and
   'foo' refer to the same dentry, since they refer to the same file)

2. a limited filename length and your filesystem truncates names (on a
   non-vfat filesystem 'dosfilen.ame' and 'dosfilename.ame' would be the
   same file and the same dentry structure).

--
Russell King ([e-mail])                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html