On Wed, 3 Jan 2007, Trond Myklebust wrote:
On Sat, 2006-12-30 at 02:04 +0100, Mikulas Patocka wrote:
On Fri, 29 Dec 2006, Trond Myklebust wrote:
On Thu, 2006-12-28 at 19:14 +0100, Mikulas Patocka wrote:
Why don't you rip off the support for colliding inode number from the
kernel at all (i.e. remove iget5_locked)?
It's reasonable to have either no support for colliding ino_t or full
support for that (including syscalls that userspace can use to work with
such filesystem) --- but I don't see any point in having half-way support
in kernel as is right now.
What would ino_t have to do with inode numbers? It is only used as a
hash table lookup. The inode number is set in the ->getattr() callback.
The question is: why does the kernel contain iget5 function that looks up
according to callback, if the filesystem cannot have more than 64-bit
inode identifier?
Huh? The filesystem can have as large a damned identifier as it likes.
NFSv4 uses 128-byte filehandles, for instance.
But then it needs some other syscall to let applications determine
hardlinks --- which was the initial topic in this thread.
POSIX filesystems are another matter. They can only have 64-bit
identifiers thanks to the requirement that inode numbers be 64-bit
unique and permanently stored, however Linux caters for a whole
truckload of filesystems which will never fit that label: look at all
those users of iunique(), for one...
I see them. The bad thing is that many programmers read POSIX, write
programs as if POSIX specification was true and these programs break
randomly on non-POSIX filesystem. Each non-POSIX filesystem invents st_ino
on its own, trying to minimize hash collision, making the failure even
less probable and worse to find.
The current situation is (for example) that cp does stat(), open(),
fstat() and compares st_ino/st_dev --- if they mismatch, it writes error
and doesn't copy files --- so if kernel removes the inode from cache
between stat() and open() and filesystem uses iunique(), cp will fail.
What utilities should the user use on those non-POSIX filesystems, if not
cp?
Probably some file-handling guidelines should be specified and written to
Documentation/ as a form of standard that can appliaction programmers use.
Mikulas
Trond
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