btrfs-progs: utils: negative numbers are more plausible than sizes over 8 EiB
diff mbox

Message ID 1480745978-24996-1-git-send-email-ce3g8jdj@umail.furryterror.org
State Superseded
Headers show

Commit Message

Zygo Blaxell Dec. 3, 2016, 6:19 a.m. UTC
I got tired of seeing "16.00EiB" whenever btrfs-progs encounters a
negative size value.

e.g. during filesystem shrink we see:

Unallocated:
   /dev/mapper/testvol0   16.00EiB

Interpreting this as a signed quantity is much more useful:

Unallocated:
   /dev/mapper/testvol0  -26.29GiB

Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
---
 utils.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

Comments

Omar Sandoval Dec. 3, 2016, 6:25 p.m. UTC | #1
On Sat, Dec 03, 2016 at 01:19:38AM -0500, Zygo Blaxell wrote:
> I got tired of seeing "16.00EiB" whenever btrfs-progs encounters a
> negative size value.
> 
> e.g. during filesystem shrink we see:
> 
> Unallocated:
>    /dev/mapper/testvol0   16.00EiB
> 
> Interpreting this as a signed quantity is much more useful:
> 
> Unallocated:
>    /dev/mapper/testvol0  -26.29GiB
> 
> Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
> ---
>  utils.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/utils.c b/utils.c
> index 69b580a..bd2b66e 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -2594,20 +2594,23 @@ static const char* unit_suffix_binary[] =
>  static const char* unit_suffix_decimal[] =
>  	{ "B", "kB", "MB", "GB", "TB", "PB", "EB"};
>  
> -int pretty_size_snprintf(u64 size, char *str, size_t str_size, unsigned unit_mode)
> +int pretty_size_snprintf(u64 usize, char *str, size_t str_size, unsigned unit_mode)
>  {
>  	int num_divs;
>  	float fraction;
> -	u64 base = 0;
> +	s64 base = 0;
>  	int mult = 0;
>  	const char** suffix = NULL;
> -	u64 last_size;
> +	s64 last_size;
>  
>  	if (str_size == 0)
>  		return 0;
>  
> +	/* Negative numbers are more plausible than sizes over 8 EiB. */
> +	s64 size = (s64)usize;

Just make pretty_size_snprintf() take an s64 size so it's clear from the
function signature that it's signed instead of hidden in the definition.

> +
>  	if ((unit_mode & ~UNITS_MODE_MASK) == UNITS_RAW) {
> -		snprintf(str, str_size, "%llu", size);
> +		snprintf(str, str_size, "%lld", size);
>  		return 0;
>  	}
>  
> @@ -2642,7 +2645,7 @@ int pretty_size_snprintf(u64 size, char *str, size_t str_size, unsigned unit_mod
>  			   num_divs = 0;
>  			   break;
>  	default:
> -		while (size >= mult) {
> +		while ((size < 0 ? -size : size) >= mult) {
>  			last_size = size;
>  			size /= mult;
>  			num_divs++;
> -- 
> 2.1.4
> 
> --
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Zygo Blaxell Dec. 3, 2016, 8:30 p.m. UTC | #2
On Sat, Dec 03, 2016 at 10:25:17AM -0800, Omar Sandoval wrote:
> On Sat, Dec 03, 2016 at 01:19:38AM -0500, Zygo Blaxell wrote:
> > I got tired of seeing "16.00EiB" whenever btrfs-progs encounters a
> > negative size value.
> > 
> > e.g. during filesystem shrink we see:
> > 
> > Unallocated:
> >    /dev/mapper/testvol0   16.00EiB
> > 
> > Interpreting this as a signed quantity is much more useful:
> > 
> > Unallocated:
> >    /dev/mapper/testvol0  -26.29GiB
> > 
> > Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
> > ---
> >  utils.c | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/utils.c b/utils.c
> > index 69b580a..bd2b66e 100644
> > --- a/utils.c
> > +++ b/utils.c
> > @@ -2594,20 +2594,23 @@ static const char* unit_suffix_binary[] =
> >  static const char* unit_suffix_decimal[] =
> >  	{ "B", "kB", "MB", "GB", "TB", "PB", "EB"};
> >  
> > -int pretty_size_snprintf(u64 size, char *str, size_t str_size, unsigned unit_mode)
> > +int pretty_size_snprintf(u64 usize, char *str, size_t str_size, unsigned unit_mode)
> >  {
> >  	int num_divs;
> >  	float fraction;
> > -	u64 base = 0;
> > +	s64 base = 0;
> >  	int mult = 0;
> >  	const char** suffix = NULL;
> > -	u64 last_size;
> > +	s64 last_size;
> >  
> >  	if (str_size == 0)
> >  		return 0;
> >  
> > +	/* Negative numbers are more plausible than sizes over 8 EiB. */
> > +	s64 size = (s64)usize;
> 
> Just make pretty_size_snprintf() take an s64 size so it's clear from the
> function signature that it's signed instead of hidden in the definition.

I intentionally buried the unsigned -> signed conversion in the lowest
level function so I wouldn't trigger signed/unsigned conversion warnings
at all 46 call sites for pretty_size_mode.  The btrfs code uses u64
endemically for all size data, and I wasn't about to try to change that.

The word "pretty" in the function name should imply that what comes out
is a possibly lossy transformation of what goes in.  Since "16.00EiB"
is much more lossy than "-29.96GiB", I believe I am merely reducing the
lossiness quantitatively rather than qualitatively.

On the other hand, the signed/unsigned warning isn't enabled by default
in this project.  I can certainly do it that way if you prefer.

> > +
> >  	if ((unit_mode & ~UNITS_MODE_MASK) == UNITS_RAW) {
> > -		snprintf(str, str_size, "%llu", size);
> > +		snprintf(str, str_size, "%lld", size);
> >  		return 0;
> >  	}
> >  
> > @@ -2642,7 +2645,7 @@ int pretty_size_snprintf(u64 size, char *str, size_t str_size, unsigned unit_mod
> >  			   num_divs = 0;
> >  			   break;
> >  	default:
> > -		while (size >= mult) {
> > +		while ((size < 0 ? -size : size) >= mult) {
> >  			last_size = size;
> >  			size /= mult;
> >  			num_divs++;
> > -- 
> > 2.1.4
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Patch
diff mbox

diff --git a/utils.c b/utils.c
index 69b580a..bd2b66e 100644
--- a/utils.c
+++ b/utils.c
@@ -2594,20 +2594,23 @@  static const char* unit_suffix_binary[] =
 static const char* unit_suffix_decimal[] =
 	{ "B", "kB", "MB", "GB", "TB", "PB", "EB"};
 
-int pretty_size_snprintf(u64 size, char *str, size_t str_size, unsigned unit_mode)
+int pretty_size_snprintf(u64 usize, char *str, size_t str_size, unsigned unit_mode)
 {
 	int num_divs;
 	float fraction;
-	u64 base = 0;
+	s64 base = 0;
 	int mult = 0;
 	const char** suffix = NULL;
-	u64 last_size;
+	s64 last_size;
 
 	if (str_size == 0)
 		return 0;
 
+	/* Negative numbers are more plausible than sizes over 8 EiB. */
+	s64 size = (s64)usize;
+
 	if ((unit_mode & ~UNITS_MODE_MASK) == UNITS_RAW) {
-		snprintf(str, str_size, "%llu", size);
+		snprintf(str, str_size, "%lld", size);
 		return 0;
 	}
 
@@ -2642,7 +2645,7 @@  int pretty_size_snprintf(u64 size, char *str, size_t str_size, unsigned unit_mod
 			   num_divs = 0;
 			   break;
 	default:
-		while (size >= mult) {
+		while ((size < 0 ? -size : size) >= mult) {
 			last_size = size;
 			size /= mult;
 			num_divs++;