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Date: Mon, 21 Sep 2015 16:54:59 +0200
From: Maurizio Lombardi <mlombard@...hat.com>
To: Rasmus Villemoes <linux@...musvillemoes.dk>,
Tejun Heo <tj@...nel.org>
Cc: joe@...ches.com, linux-kernel@...r.kernel.org,
linux-scsi@...r.kernel.org, dgilbert@...erlog.com
Subject: Re: [RFC PATCH 0/3] fix *pbl format support
Hi Rasmus,
On 09/16/2015 10:35 PM, Rasmus Villemoes wrote:
>
> I just remembered: I noticed a while ago that the qualifier member is
> only used inside format_decode (in the end, the information is folded
> into the type member), so one might as well use a local variable for
> that. This gives option (3): Make field_width a 24 bit bitfield. I think
> that should be sufficient for any realistic bitmap that one would
> print. The patch is also rather small. Surprisingly, bloat-o-meter even
> says that it's also a net win in code size:
I tested your patch with scsi-debug and it works for me:
# modprobe scsi-debug dev_size_mb=256 lbpu=1 lbpws10=1
# cat /sys/bus/pseudo/drivers/scsi_debug/map
# vgcreate tsvg /dev/sdb
Physical volume "/dev/sdb" successfully created
Volume group "tsvg" successfully created
# cat /sys/bus/pseudo/drivers/scsi_debug/map
0-15
# lvcreate -V200m -l99%FREE -T tsvg/pool -n lv1 --discards ignore
Logical volume "lv1" created.
# cat /sys/bus/pseudo/drivers/scsi_debug/map
0-31,2048-2055,501760-501871
Thanks,
Maurizio Lombardi
>
> add/remove: 18/16 grow/shrink: 3/2 up/down: 5551/-5775 (-224)
>
> (the huge absolute numbers are due to stuff like
>
> pointer - 1148 +1148
> pointer.isra 1116 - -1116
>
> so the functions haven't actually changed that much). I'll have to check
> how this can be (smaller might still be worse), but at least it doesn't
> seem to be a catastrophe in terms of .text bloat.
>
> [Grr, why don't we have a way to do a compile-time assert outside
> function context?]
>
> Only compile-tested.
>
> From: Rasmus Villemoes <linux@...musvillemoes.dk>
> Date: Wed, 16 Sep 2015 22:06:14 +0200
> Subject: [RFC] lib/vsprintf.c: expand field_width to 24 bits
>
> Maurizio Lombardi reported a problem with the %pb extension: It
> doesn't work for sufficiently large bitmaps, since the size is stashed
> in the field_width field of the struct printf_spec, which is currently
> an s16. Concretely, this manifested itself in
> /sys/bus/pseudo/drivers/scsi_debug/map being empty, since the bitmap
> printer got a size of 0, which is the 16 bit truncation of the actual
> bitmap size.
>
> We do want to keep struct printf_spec at 8 bytes so that it can
> cheaply be passed by value. The qualifier field is only used for
> internal bookkeeping in format_decode, so we might as well use a local
> variable for that. This gives us an additional 8 bits, which we can
> then use for the field width. To stay in 8 bytes, we need to do a
> little rearranging and make the type member a bitfield as well.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
> lib/vsprintf.c | 33 +++++++++++++++++----------------
> 1 file changed, 17 insertions(+), 16 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 95cd63b43b99..cce2a780a82e 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -380,13 +380,13 @@ enum format_type {
> };
>
> struct printf_spec {
> - u8 type; /* format_type enum */
> + u8 type:8; /* format_type enum */
> + s32 field_width:24; /* width of output field */
> u8 flags; /* flags to number() */
> u8 base; /* number base, 8, 10 or 16 only */
> - u8 qualifier; /* number qualifier, one of 'hHlLtzZ' */
> - s16 field_width; /* width of output field */
> s16 precision; /* # of digits/chars */
> };
> +extern char __check_printf_spec[1-2*(sizeof(struct printf_spec) != 8)];
>
> static noinline_for_stack
> char *number(char *buf, char *end, unsigned long long num,
> @@ -1633,6 +1633,7 @@ static noinline_for_stack
> int format_decode(const char *fmt, struct printf_spec *spec)
> {
> const char *start = fmt;
> + char qualifier;
>
> /* we finished early by reading the field width */
> if (spec->type == FORMAT_TYPE_WIDTH) {
> @@ -1715,16 +1716,16 @@ precision:
>
> qualifier:
> /* get the conversion qualifier */
> - spec->qualifier = -1;
> + qualifier = 0;
> if (*fmt == 'h' || _tolower(*fmt) == 'l' ||
> _tolower(*fmt) == 'z' || *fmt == 't') {
> - spec->qualifier = *fmt++;
> - if (unlikely(spec->qualifier == *fmt)) {
> - if (spec->qualifier == 'l') {
> - spec->qualifier = 'L';
> + qualifier = *fmt++;
> + if (unlikely(qualifier == *fmt)) {
> + if (qualifier == 'l') {
> + qualifier = 'L';
> ++fmt;
> - } else if (spec->qualifier == 'h') {
> - spec->qualifier = 'H';
> + } else if (qualifier == 'h') {
> + qualifier = 'H';
> ++fmt;
> }
> }
> @@ -1781,19 +1782,19 @@ qualifier:
> return fmt - start;
> }
>
> - if (spec->qualifier == 'L')
> + if (qualifier == 'L')
> spec->type = FORMAT_TYPE_LONG_LONG;
> - else if (spec->qualifier == 'l') {
> + else if (qualifier == 'l') {
> BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG);
> spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN);
> - } else if (_tolower(spec->qualifier) == 'z') {
> + } else if (_tolower(qualifier) == 'z') {
> spec->type = FORMAT_TYPE_SIZE_T;
> - } else if (spec->qualifier == 't') {
> + } else if (qualifier == 't') {
> spec->type = FORMAT_TYPE_PTRDIFF;
> - } else if (spec->qualifier == 'H') {
> + } else if (qualifier == 'H') {
> BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE);
> spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN);
> - } else if (spec->qualifier == 'h') {
> + } else if (qualifier == 'h') {
> BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT);
> spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN);
> } else {
>
--
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