Re: [f2fs-dev] [PATCH 1/1] f2fs: fix args passed to trace_f2fs_lookup_end

From: Chao Yu
Date: Mon May 29 2023 - 06:19:04 EST

On 2023/5/29 12:13, Wu Bo wrote:
On Sat, May 27, 2023 at 09:01:41AM +0800, Chao Yu wrote:
On 2023/5/27 1:21, Jaegeuk Kim wrote:
On 05/24, Wu Bo wrote:
The NULL return of 'd_splice_alias' dosen't mean error.

Signed-off-by: Wu Bo <bo.wu@xxxxxxxx>
fs/f2fs/namei.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
index 77a71276ecb1..e5a3e39ce90c 100644
--- a/fs/f2fs/namei.c
+++ b/fs/f2fs/namei.c
@@ -577,7 +577,7 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
new = c(inode, dentry);
err = PTR_ERR_OR_ZERO(new);
- trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
+ trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);

Shouldn't give an error pointer to the dentry field.

How about just giving the err?

- err = PTR_ERR_OR_ZERO(new);
- trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
+ trace_f2fs_lookup_end(dir, dentry, ino, PTR_ERR_OR_ZERO(new));

static inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
if (IS_ERR(ptr))
return PTR_ERR(ptr);
return 0;

For below two cases, PTR_ERR_OR_ZERO(new) will return zero:
a) f2fs_lookup found existed dentry
b) f2fs_lookup didn't find existed dentry (-ENOENT case)

So in below commit, I passed -ENOENT to tracepoint for case b), so we can
distinguish result of f2fs_lookup in tracepoint, actually, -ENOENT is expected
value when we create a new file/directory.

Commit 84597b1f9b05 ("f2fs: fix wrong value of tracepoint parameter")
I can see this commit is try to distinguish the dentry not existed case.
But a normal case which dentry is exactly found will also go through
'd_splice_alias', and its return is also NULL. This makes the tracepoint always
print 'err:-2' like the following:
ls-11676 [004] .... 329281.943118: f2fs_lookup_end: dev = (254,39), pino = 4451, name:Alarms, ino:7093, err:-2
ls-11676 [004] .... 329281.943145: f2fs_lookup_end: dev = (254,39), pino = 4451, name:Notifications, ino:7094, err:-2
ls-11676 [004] .... 329281.943172: f2fs_lookup_end: dev = (254,39), pino = 4451, name:Pictures, ino:7095, err:-2
Even these lookup are acctually successful, this is a bit strange.

Ah, I misunderstand return value's meaning of .lookup.

So, how about this? it only update err if d_splice_alias() returns a negative

if (IS_ERR(new))
err = PTR_ERR(new);
trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);


return new;

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