Re: making an in-memory hashing table ["name" -> ino_t] with thousands of entries

[Luke Kenneth Casson Leighton]

On Fri, Oct 01, 2004 at 02:30:19PM +0200, Martin Waitz wrote:
> hi :)

 hello martin: thanks for responding.

> On Fri, Oct 01, 2004 at 01:02:22PM +0100, Luke Kenneth Casson Leighton wrote:
> > bearing in mind that for every file accessed via a fuse
> > filesystem, a cache entry is created, and therefore the number
> > of entries could potentially run into hundreds of thousands
> > of entries.
> 
> but these can be cleaned if needed.
> 
> why do you have to move all inodes into the kernel when the kernel
> already cache those that are really needed?
> (perhaps I'm misunderstandig fuses role here)
 
 fuse is a userspace filesystem.

 it can be absolutely anything.

 however, the author of fuse, in order to simplify the userspace
 interface, manages the userspace-inode <-> userspace-fullpathnames
 in a library.

 for the sake of argument, let's call this the fuse-inode-cache.

 entries in the fuse-inode-cache must be persistent for as long as a
 filename exists on the userspace file system.

 also, if an entry happens not to exist at the time a lookup
 is done, then an entry into the cache is created, associating that full
 path name with a newly created unique inode number (in the userspace
 fuse-inode-cache).

 then, that information (the unique inode number) is communicated _back_
 to the fuse module, along with the stat information (yes, a userspace
 lstat is done as well), and the kernel's inode structure is updated
 from that information.


 anyway: for various reasons, inside the kernel, it must
 be possible to do a lookup from the full path name to the
 inode number.


 smbfs suffers from exactly the same problem: inodes don't exist on the
 SMB protocol.

 hm, i wonder if i should just rip stacks of code from the smbfs kernel
 module?

 i note with interest the existence of a function smb_refresh_inode()
 which gets passed a dentry.

 then i can do a getattr and go from there.

 oh, man, this is hair-raising stuff.

 l.

 

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