[PATCH 0/3] 32/64 bit llseek hashes

With the ext3/ext4 directory index implementation hashes are used to specify
offsets for llseek(). For compatibility with NFSv2 and 32-bit user space
on 64-bit systems (kernel space) ext3/ext4 currently only return 32-bit 
hashes and therefore the probability of hash collisions for larger directories
is rather high. As recently reported on the NFS mailing list that theoretical
problem also happens on real systems:
http://comments.gmane.org/gmane.linux.nfs/40863

The following series adds two new open flags to tell ext4
to to 32-bit or 64-bit hash values for llseek() calls.
These flags are then used by NFS to use 32-bit (NFSv2) or 64-bit
offsets (hashes in case of ext3/ext4) for readdir and seekdir.
User space does not need to specify these flags, but usually the check
for is_32bit_api() should be sufficient.

---

Bernd Schubert (2):
      Remove check for a 32-bit cookie in nfsd4_readdir()
      nfsd: vfs_llseek() with O_32BITHASH or O_64BITHASH

Fan Yong (1):
      Return 32/64-bit dir name hash according to usage type


 fs/ext4/dir.c               |  160 ++++++++++++++++++++++++++++++++++---------
 fs/fcntl.c                  |    5 +
 fs/nfsd/nfs4proc.c          |    2 -
 fs/nfsd/vfs.c               |    6 ++
 include/asm-generic/fcntl.h |    9 ++
 5 files changed, 145 insertions(+), 37 deletions(-)

-- 
Bernd Schubert

Use 32-bit or 64-bit llseek() hashes for directory offsets depending on
the NFS version. NFSv2 gets 32-bit hashes only.

Signed-off-by: Bernd Schubert <redacted>
---
 fs/nfsd/vfs.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index fd0acca..d79bbcd 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c

@@ -1994,6 +1994,12 @@ nfsd_readdir(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t *offsetp,
 	if (err)
 		goto out;
 
+	/* NFSv2 only supports 32 bit cookies */
+	if (rqstp->rq_vers > 2)
+		file->f_flags &= O_64BITHASH;
+	else
+		file->f_flags &= O_32BITHASH;
+
 	offset = vfs_llseek(file, offset, 0);
 	if (offset < 0) {
 		err = nfserrno((int)offset);