[RFC][PATCH v3 06/55] handle_mounts(): start building a sane wrapper for follow_managed()

Al Viro
2020-03-01T21:52:47Z

All callers of follow_managed() follow it on success with the same steps -
d_backing_inode(path->dentry) is calculated and stored into some struct inode *
variable and, in all but one case, an unsigned variable (nd->seq to be) is
zeroed. The single exception is lookup_fast() and there zeroing is correct
thing to do - not doing it is a pointless microoptimization.

Add a wrapper for follow_managed() that would do that combination.
It's mostly a vehicle for code massage - it will be changing quite a bit,
and the current calling conventions are by no means final. Right now it
takes path, nameidata and (as out params) inode and seq, similar to
__follow_mount_rcu(). Which will soon get folded into it...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 6938d20aa73a..c104ec75faef 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1385,6 +1385,18 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
!(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
}

+static inline int handle_mounts(struct path *path, struct nameidata *nd,
+ struct inode **inode, unsigned int *seqp)
+{
+ int ret = follow_managed(path, nd);
+
+ if (likely(ret >= 0)) {
+ *inode = d_backing_inode(path->dentry);
+ *seqp = 0; /* out of RCU mode, so the value doesn't matter */
+ }
+ return ret;
+}
+
static int follow_dotdot_rcu(struct nameidata *nd)
{
struct inode *inode = nd->inode;
@@ -1607,7 +1619,6 @@ static int lookup_fast(struct nameidata *nd,
struct vfsmount *mnt = nd->path.mnt;
struct dentry *dentry, *parent = nd->path.dentry;
int status = 1;
- int err;

/*
* Rename seqlock is not required here because in the off chance
@@ -1677,10 +1688,7 @@ static int lookup_fast(struct nameidata *nd,

path->mnt = mnt;
path->dentry = dentry;
- err = follow_managed(path, nd);
- if (likely(err > 0))
- *inode = d_backing_inode(path->dentry);
- return err;
+ return handle_mounts(path, nd, inode, seqp);
}

/* Fast lookup failed, do it the slow way */
@@ -1875,12 +1883,9 @@ static int walk_component(struct nameidata *nd, int flags)
return PTR_ERR(path.dentry);

path.mnt = nd->path.mnt;
- err = follow_managed(&path, nd);
+ err = handle_mounts(&path, nd, &inode, &seq);
if (unlikely(err < 0))
return err;
-
- seq = 0; /* we are already out of RCU mode */
- inode = d_backing_inode(path.dentry);
}

return step_into(nd, &path, flags, inode, seq);
@@ -2365,11 +2370,9 @@ static int handle_lookup_down(struct nameidata *nd)
return -ECHILD;
} else {
dget(path.dentry);
- err = follow_managed(&path, nd);
+ err = handle_mounts(&path, nd, &inode, &seq);
if (unlikely(err < 0))
return err;
- inode = d_backing_inode(path.dentry);
- seq = 0;
}
path_to_nameidata(&path, nd);
nd->inode = inode;
@@ -3392,12 +3395,9 @@ static int do_last(struct nameidata *nd,
got_write = false;
}

- error = follow_managed(&path, nd);
+ error = handle_mounts(&path, nd, &inode, &seq);
if (unlikely(error < 0))
return error;
-
- seq = 0; /* out of RCU mode, so the value doesn't matter */
- inode = d_backing_inode(path.dentry);
finish_lookup:
error = step_into(nd, &path, 0, inode, seq);
if (unlikely(error))
--
2.11.0