[PATCH] CacheFiles: Cleanup redundant tests on unsigned

[PATCH] CacheFiles: Cleanup redundant tests on unsigned

[Roel Kluin]

The variables are unsigned so the test `>= 0' is always true,
the `< 0' test always fails. The other part of
the test catches wrapped values.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
 fs/cachefiles/bind.c   |    6 ++----
 fs/cachefiles/daemon.c |    6 +++---
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/cachefiles/bind.c b/fs/cachefiles/bind.c
index 3797e00..ce776f6 100644
--- a/fs/cachefiles/bind.c
+++ b/fs/cachefiles/bind.c
@@ -39,13 +39,11 @@ int cachefiles_daemon_bind(struct cachefiles_cache *cache, char *args)
 	       args);
 
 	/* start by checking things over */
-	ASSERT(cache->fstop_percent >= 0 &&
-	       cache->fstop_percent < cache->fcull_percent &&
+	ASSERT(cache->fstop_percent < cache->fcull_percent &&
 	       cache->fcull_percent < cache->frun_percent &&
 	       cache->frun_percent  < 100);
 
-	ASSERT(cache->bstop_percent >= 0 &&
-	       cache->bstop_percent < cache->bcull_percent &&
+	ASSERT(cache->bstop_percent < cache->bcull_percent &&
 	       cache->bcull_percent < cache->brun_percent &&
 	       cache->brun_percent  < 100);
 
diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 4618516..bb30d01 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -220,7 +220,7 @@ static ssize_t cachefiles_daemon_write(struct file *file,
 	if (test_bit(CACHEFILES_DEAD, &cache->flags))
 		return -EIO;
 
-	if (datalen < 0 || datalen > PAGE_SIZE - 1)
+	if (datalen > PAGE_SIZE - 1)
 		return -EOPNOTSUPP;
 
 	/* drag the command string into the kernel so we can parse it */
@@ -385,7 +385,7 @@ static int cachefiles_daemon_fstop(struct cachefiles_cache *cache, char *args)
 	if (args[0] != '%' || args[1] != '\0')
 		return -EINVAL;
 
-	if (fstop < 0 || fstop >= cache->fcull_percent)
+	if (fstop >= cache->fcull_percent)
 		return cachefiles_daemon_range_error(cache, args);
 
 	cache->fstop_percent = fstop;
@@ -457,7 +457,7 @@ static int cachefiles_daemon_bstop(struct cachefiles_cache *cache, char *args)
 	if (args[0] != '%' || args[1] != '\0')
 		return -EINVAL;
 
-	if (bstop < 0 || bstop >= cache->bcull_percent)
+	if (bstop >= cache->bcull_percent)
 		return cachefiles_daemon_range_error(cache, args);
 
 	cache->bstop_percent = bstop;

[PATCH] CacheFiles: Cleanup redundant tests on unsigned

[David Howells]

From: Roel Kluin <roel.kluin@gmail.com>

The variables are unsigned so the test `>= 0' is always true,
the `< 0' test always fails. The other part of
the test catches wrapped values.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/cachefiles/bind.c   |    6 ++----
 fs/cachefiles/daemon.c |    6 +++---
 2 files changed, 5 insertions(+), 7 deletions(-)


diff --git a/fs/cachefiles/bind.c b/fs/cachefiles/bind.c
index 3797e00..ce776f6 100644
--- a/fs/cachefiles/bind.c
+++ b/fs/cachefiles/bind.c
@@ -39,13 +39,11 @@ int cachefiles_daemon_bind(struct cachefiles_cache *cache, char *args)
 	       args);
 
 	/* start by checking things over */
-	ASSERT(cache->fstop_percent >= 0 &&
-	       cache->fstop_percent < cache->fcull_percent &&
+	ASSERT(cache->fstop_percent < cache->fcull_percent &&
 	       cache->fcull_percent < cache->frun_percent &&
 	       cache->frun_percent  < 100);
 
-	ASSERT(cache->bstop_percent >= 0 &&
-	       cache->bstop_percent < cache->bcull_percent &&
+	ASSERT(cache->bstop_percent < cache->bcull_percent &&
 	       cache->bcull_percent < cache->brun_percent &&
 	       cache->brun_percent  < 100);
 
diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 4618516..bb30d01 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -220,7 +220,7 @@ static ssize_t cachefiles_daemon_write(struct file *file,
 	if (test_bit(CACHEFILES_DEAD, &cache->flags))
 		return -EIO;
 
-	if (datalen < 0 || datalen > PAGE_SIZE - 1)
+	if (datalen > PAGE_SIZE - 1)
 		return -EOPNOTSUPP;
 
 	/* drag the command string into the kernel so we can parse it */
@@ -385,7 +385,7 @@ static int cachefiles_daemon_fstop(struct cachefiles_cache *cache, char *args)
 	if (args[0] != '%' || args[1] != '\0')
 		return -EINVAL;
 
-	if (fstop < 0 || fstop >= cache->fcull_percent)
+	if (fstop >= cache->fcull_percent)
 		return cachefiles_daemon_range_error(cache, args);
 
 	cache->fstop_percent = fstop;
@@ -457,7 +457,7 @@ static int cachefiles_daemon_bstop(struct cachefiles_cache *cache, char *args)
 	if (args[0] != '%' || args[1] != '\0')
 		return -EINVAL;
 
-	if (bstop < 0 || bstop >= cache->bcull_percent)
+	if (bstop >= cache->bcull_percent)
 		return cachefiles_daemon_range_error(cache, args);
 
 	cache->bstop_percent = bstop;

Re: [PATCH] CacheFiles: Cleanup redundant tests on unsigned

[Linus Torvalds]

On Mon, 26 Oct 2009, David Howells wrote:
>
> From: Roel Kluin <roel.kluin@gmail.com>
> 
> The variables are unsigned so the test `>= 0' is always true,
> the `< 0' test always fails. The other part of
> the test catches wrapped values.

This is an excellent example of why I think that some gcc warnings are 
pure and utter sh*t, and why just blindly trying to avoid them then leads 
to worse code.

> -	if (datalen < 0 || datalen > PAGE_SIZE - 1)
> +	if (datalen > PAGE_SIZE - 1)
> -	if (fstop < 0 || fstop >= cache->fcull_percent)
> +	if (fstop >= cache->fcull_percent)
> -	if (bstop < 0 || bstop >= cache->bcull_percent)
> +	if (bstop >= cache->bcull_percent)

You've now actively made the code more fragile, only to avoid a warning.

The old code was clearly correct. The new code subtle depends on the type 
of comparison. 

I _hate_ those idiotic warnings, and in this case the "warning-free" code 
is actively worse than the original.

A smart compiler would see that it's a range check, and one that could 
have been done as an unsigned comparison (well, for the constant compare 
case) regardless of the type of the variable being tested. So a _smart_ 
compiler wouldn't complain, but it might use the signedness information to 
silently simplify the comparison.

A _stupid_ compiler complains, and thus forces people to either ignore the 
warning, or make the code worse.

Which one would you prefer?

		Linus