So, it seems there's some concensus building here, and it seems that
I've become the chosen victi^wvolunteer for this. So, here's a patch.
It's missing a Guns-supplied-by: tag though.
From: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Subject: Mark IS_ERR_OR_NULL() deprecated
IS_ERR_OR_NULL() attracts a lot of abuse: people use it without much
thought about it's effects. Common errors include:
1. checking the returned pointer for functions defined as only
returning errno-pointer values, rather than using IS_ERR().
This leads to: ptr = foo(); if (IS_ERR_OR_NULL(ptr)) return
PTR_ERR(ptr);
2. using it to check functions which only ever return NULL on error,
thereby leading to another zero-error value return.
In the case of debugfs functions, these return errno-pointer values when
debugfs is configured out, which means code which blindly checks using
IS_ERR_OR_NULL() ends up returning errors, which is rather perverse for
something that's not implemented.
Therefore, let's schedule it for removal in a few releases.
Nicolas Pitre comments:
> I do agree with Russell here. Despite the original intentions behind
> IS_ERR_OR_NULL() which were certainly legitimate, the end result in
> practice is less reliable code with increased maintenance costs.
> Unlike other convenience macros in the kernel, this one is giving a
> false sense of correctness with too many people falling in the trap
> of using it just because it is available.
>
> I strongly think this macro should simply be removed from the source
> tree entirely and the code reverted to explicit tests against NULL
> when appropriate.
Suggested-by: David Howells <dhowells@xxxxxxxxxx>
Tape-measuring-service-offered-by: Will Deacon <will.deacon@xxxxxxx>
Victim-for-firing-sqad: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
---
Ok, so I'm in the firing line for suggesting this, but it appears
several people wish this to happen.
I'm not intending to push this patch forwards _just_ yet: we need to
sort out the existing users _first_ to prevent the kernel turning into
one hell of a mess of warnings.
include/linux/err.h | 17 ++++++++++++++++-
1 files changed, 16 insertions(+), 1 deletions(-)
diff --git a/include/linux/err.h b/include/linux/err.h
index f2edce2..d5a85df 100644
--- a/include/linux/err.h
+++ b/include/linux/err.h
@@ -34,7 +34,22 @@ static inline long __must_check IS_ERR(const void *ptr)
return IS_ERR_VALUE((unsigned long)ptr);
}
-static inline long __must_check IS_ERR_OR_NULL(const void *ptr)
+/*
+ * IS_ERR_OR_NULL() attracts a lot of abuse: people use it without much
+ * thought about it's effects. Common errors include:
+ * 1. checking the returned pointer for functions defined as only returning
+ * errno-pointer values, rather than using IS_ERR().
+ * This leads to: ptr = foo(); if (IS_ERR_OR_NULL(ptr)) return PTR_ERR(ptr);
+ * 2. using it to check functions which only ever return NULL on error,
+ * thereby leading to another zero-error value return.
+ * In the case of debugfs functions, these return errno-pointer values when
+ * debugfs is configured out, which means code which blindly checks using
+ * IS_ERR_OR_NULL() ends up returning errors, which is rather perverse for
+ * something that's not implemented.
+ *
+ * Therefore, let's schedule it for removal in a few releases.
+ */
+static inline long __must_check __deprecated IS_ERR_OR_NULL(const void *ptr)
{
return !ptr || IS_ERR_VALUE((unsigned long)ptr);
}
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