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namei: untanlge lookup_fast()

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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2016-03-05 21:32:53 -05:00
parent 6c51e513a3
commit 5d0f49c136
1 changed files with 37 additions and 46 deletions
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83
fs/namei.c
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@ -1512,32 +1512,29 @@ static struct dentry *__lookup_hash(struct qstr *name,
return lookup_real(base->d_inode, dentry, flags);
}
/*
* It's more convoluted than I'd like it to be, but... it's still fairly
* small and for now I'd prefer to have fast path as straight as possible.
* It _is_ time-critical.
*/
static int lookup_fast(struct nameidata *nd,
struct path *path, struct inode **inode,
unsigned *seqp)
{
struct vfsmount *mnt = nd->path.mnt;
struct dentry *dentry, *parent = nd->path.dentry;
int need_reval = 1;
int status = 1;
int err;
/*
* Rename seqlock is not required here because in the off chance
* of a false negative due to a concurrent rename, we're going to
* do the non-racy lookup, below.
* of a false negative due to a concurrent rename, the caller is
* going to fall back to non-racy lookup.
*/
if (nd->flags & LOOKUP_RCU) {
unsigned seq;
bool negative;
dentry = __d_lookup_rcu(parent, &nd->last, &seq);
if (!dentry)
goto unlazy;
if (unlikely(!dentry)) {
if (unlazy_walk(nd, NULL, 0))
return -ECHILD;
return 1;
}
/*
* This sequence count validates that the inode matches
@ -1545,7 +1542,7 @@ static int lookup_fast(struct nameidata *nd,
*/
*inode = d_backing_inode(dentry);
negative = d_is_negative(dentry);
if (read_seqcount_retry(&dentry->d_seq, seq))
if (unlikely(read_seqcount_retry(&dentry->d_seq, seq)))
return -ECHILD;
/*
@ -1555,63 +1552,57 @@ static int lookup_fast(struct nameidata *nd,
* The memory barrier in read_seqcount_begin of child is
* enough, we can use __read_seqcount_retry here.
*/
if (__read_seqcount_retry(&parent->d_seq, nd->seq))
if (unlikely(__read_seqcount_retry(&parent->d_seq, nd->seq)))
return -ECHILD;
*seqp = seq;
if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
status = d_revalidate(dentry, nd->flags);
if (unlikely(status <= 0)) {
if (status != -ECHILD)
need_reval = 0;
goto unlazy;
}
if (unlikely(status <= 0)) {
if (unlazy_walk(nd, dentry, seq))
return -ECHILD;
if (status == -ECHILD)
status = d_revalidate(dentry, nd->flags);
} else {
/*
* Note: do negative dentry check after revalidation in
* case that drops it.
*/
if (unlikely(negative))
return -ENOENT;
path->mnt = mnt;
path->dentry = dentry;
if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
return 0;
if (unlazy_walk(nd, dentry, seq))
return -ECHILD;
}
/*
* Note: do negative dentry check after revalidation in
* case that drops it.
*/
if (negative)
return -ENOENT;
path->mnt = mnt;
path->dentry = dentry;
if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
return 0;
unlazy:
if (unlazy_walk(nd, dentry, seq))
return -ECHILD;
} else {
dentry = __d_lookup(parent, &nd->last);
if (unlikely(!dentry))
return 1;
if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
status = d_revalidate(dentry, nd->flags);
}
if (unlikely(!dentry))
goto need_lookup;
if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval)
status = d_revalidate(dentry, nd->flags);
if (unlikely(status <= 0)) {
if (status < 0) {
dput(dentry);
return status;
if (!status) {
d_invalidate(dentry);
status = 1;
}
d_invalidate(dentry);
dput(dentry);
goto need_lookup;
return status;
}
if (unlikely(d_is_negative(dentry))) {
dput(dentry);
return -ENOENT;
}
path->mnt = mnt;
path->dentry = dentry;
err = follow_managed(path, nd);
if (likely(!err))
*inode = d_backing_inode(path->dentry);
return err;
need_lookup:
return 1;
}
/* Fast lookup failed, do it the slow way */