From 12f8ad4b0533d9212cb1d5e58ed73d2170114785 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 4 May 2012 14:59:14 -0700 Subject: vfs: clean up __d_lookup_rcu() and dentry_cmp() interfaces The calling conventions for __d_lookup_rcu() and dentry_cmp() are annoying in different ways, and there is actually one single underlying reason for both of the annoyances. The fundamental reason is that we do the returned dentry sequence number check inside __d_lookup_rcu() instead of doing it in the caller. This results in two annoyances: - __d_lookup_rcu() now not only needs to return the dentry and the sequence number that goes along with the lookup, it also needs to return the inode pointer that was validated by that sequence number check. - and because we did the sequence number check early (to validate the name pointer and length) we also couldn't just pass the dentry itself to dentry_cmp(), we had to pass the counted string that contained the name. So that sequence number decision caused two separate ugly calling conventions. Both of these problems would be solved if we just did the sequence number check in the caller instead. There's only one caller, and that caller already has to do the sequence number check for the parent anyway, so just do that. That allows us to stop returning the dentry->d_inode in that in-out argument (pointer-to-pointer-to-inode), so we can make the inode argument just a regular input inode pointer. The caller can just load the inode from dentry->d_inode, and then do the sequence number check after that to make sure that it's synchronized with the name we looked up. And it allows us to just pass in the dentry to dentry_cmp(), which is what all the callers really wanted. Sure, dentry_cmp() has to be a bit careful about the dentry (which is not stable during RCU lookup), but that's actually very simple. And now that dentry_cmp() can clearly see that the first string argument is a dentry, we can use the direct word access for that, instead of the careful unaligned zero-padding. The dentry name is always properly aligned, since it is a single path component that is either embedded into the dentry itself, or was allocated with kmalloc() (see __d_alloc). Finally, this also uninlines the nasty slow-case for dentry comparisons: that one *does* need to do a sequence number check, since it will call in to the low-level filesystems, and we want to give those a stable inode pointer and path component length/start arguments. Doing an extra sequence check for that slow case is not a problem, though. Signed-off-by: Linus Torvalds --- include/linux/dcache.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 7e11f1418203..8239f64d1c2e 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -282,7 +282,7 @@ extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *); extern struct dentry *__d_lookup(struct dentry *, struct qstr *); extern struct dentry *__d_lookup_rcu(const struct dentry *parent, const struct qstr *name, - unsigned *seq, struct inode **inode); + unsigned *seq, struct inode *inode); /** * __d_rcu_to_refcount - take a refcount on dentry if sequence check is ok -- cgit v1.2.3 From 26fe575028703948880fce4355a210c76bb0536e Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Thu, 10 May 2012 13:14:12 -0700 Subject: vfs: make it possible to access the dentry hash/len as one 64-bit entry This allows comparing hash and len in one operation on 64-bit architectures. Right now only __d_lookup_rcu() takes advantage of this, since that is the case we care most about. The use of anonymous struct/unions hides the alternate 64-bit approach from most users, the exception being a few cases where we initialize a 'struct qstr' with a static initializer. This makes the problematic cases use a new QSTR_INIT() helper function for that (but initializing just the name pointer with a "{ .name = xyzzy }" initializer remains valid, as does just copying another qstr structure). Signed-off-by: Linus Torvalds --- include/linux/dcache.h | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 8239f64d1c2e..094789ff3e9f 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -25,6 +25,13 @@ struct vfsmount; #define IS_ROOT(x) ((x) == (x)->d_parent) +/* The hash is always the low bits of hash_len */ +#ifdef __LITTLE_ENDIAN + #define HASH_LEN_DECLARE u32 hash; u32 len; +#else + #define HASH_LEN_DECLARE u32 len; u32 hash; +#endif + /* * "quick string" -- eases parameter passing, but more importantly * saves "metadata" about the string (ie length and the hash). @@ -33,11 +40,19 @@ struct vfsmount; * dentry. */ struct qstr { - unsigned int hash; - unsigned int len; + union { + struct { + HASH_LEN_DECLARE; + }; + u64 hash_len; + }; const unsigned char *name; }; +#define QSTR_INIT(n,l) { { { .len = l } }, .name = n } +#define hashlen_hash(hashlen) ((u32) (hashlen)) +#define hashlen_len(hashlen) ((u32)((hashlen) >> 32)) + struct dentry_stat_t { int nr_dentry; int nr_unused; -- cgit v1.2.3