Russell Cattelan wrote:
Wendy Cheng wrote:
Linux kernel, particularly the VFS layer, is starting to show signs
of inadequacy as the software components built upon it keep growing.
I have doubts that it can keep up and handle this complexity with a
development policy like you just described (filesystem is a dumb
layer ?). Aren't these DIO_xxx_LOCKING flags inside
__blockdev_direct_IO() a perfect example why trying to do too many
things inside vfs layer for so many filesystems is a bad idea ? By
the way, since we're on this subject, could we discuss a little bit
about vfs rename call (or I can start another new discussion thread) ?
Note that linux do_rename() starts with the usual lookup logic,
followed by "lock_rename", then a final round of dentry lookup, and
finally comes to filesystem's i_op->rename call. Since lock_rename()
only calls for vfs layer locks that are local to this particular
machine, for a cluster filesystem, there exists a huge window between
the final lookup and filesystem's i_op->rename calls such that the
file could get deleted from another node before fs can do anything
about it. Is it possible that we could get a new function pointer
(lock_rename) in inode_operations structure so a cluster filesystem
can do proper locking ?
It looks like the ocfs2 guys have the similar problem?
http://ftp.kernel.org/pub/linux/kernel/people/mfasheh/ocfs2/ocfs2_git_patches/ocfs2-upstream-linus-20060924/0009-PATCH-Allow-file-systems-to-manually-d_move-inside-of-rename.txt
Thanks for the pointer. Same as ocfs2, under current VFS code, both
GFS1/2 also need FS_ODD_RENAME flag for the rename problem - got an ugly
~200 line draft patch ready for GFS1 (and am looking into GFS2 at this
moment). The issue here is, for GFS, if vfs lock_rename() can call us,
this complication can be greatly reduced. Will start another thread to
see whether the wish can be granted.
-- Wendy
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