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Message-ID: <20150510135203.GC1717@p183.telecom.by>
Date: Sun, 10 May 2015 16:52:03 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux@...musvillemoes.dk
Subject: Re: [PATCH 02/12] Add parse_integer() (replacement for
simple_strto*())
On Fri, May 08, 2015 at 01:46:46PM -0700, Andrew Morton wrote:
> On Fri, 8 May 2015 21:30:29 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> > kstrto*() and kstrto*_from_user() family of functions were added
> > to help with parsing one integer written as string to proc/sysfs/debugfs
> > files. But they have a limitation: string passed must end with \0 or \n\0.
> > There are enough places where kstrto*() functions can't be used because of
> > this limitation. Trivial example: major:minor "%u:%u".
> >
> > Currently the only way to parse everything is simple_strto*() functions.
> > But they are suboptimal:
> > * they do not detect overflow (can be fixed, but no one bothered since ~0.99.11),
> > * there are only 4 of them -- long and "long long" versions,
> > This leads to silent truncation in the most simple case:
> >
> > val = strtoul(s, NULL, 0);
> >
> > * half of the people think that "char **endp" argument is necessary and
> > add unnecessary variable.
> >
> > OpenBSD people, fed up with how complex correct integer parsing is, added
> > strtonum(3) to fixup for deficiencies of libc-style integer parsing:
> > http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man3/strtonum.3?query=strtonum&arch=i386
> >
> > It'd be OK to copy that but it relies on "errno" and fixed strings as
> > error reporting channel which I think is not OK for kernel.
> > strtonum() also doesn't report number of characted consumed.
> >
> > What to do?
> >
> > Enter parse_integer().
>
> fs/binfmt_misc.c | 12
> fs/cachefiles/daemon.c | 84 ++--
> fs/dcache.c | 2
> fs/ext2/super.c | 6
> fs/ext3/super.c | 7
> fs/ext4/super.c | 15
> fs/inode.c | 2
> fs/libfs.c | 26 -
> fs/namespace.c | 4
> fs/ocfs2/cluster/heartbeat.c | 54 +-
> fs/ocfs2/cluster/nodemanager.c | 50 +-
> fs/ocfs2/stack_user.c | 52 +-
> include/linux/kernel.h | 129 -------
> include/linux/parse-integer.h | 188 ++++++++++
> lib/Kconfig.debug | 3
> lib/Makefile | 2
> lib/cmdline.c | 42 +-
> lib/kstrtox.c | 254 -------------
> lib/kstrtox.h | 1
> lib/parse-integer.c | 222 ++++++++++++
> lib/parser.c | 33 -
> lib/swiotlb.c | 2
> lib/test-kstrtox.c | 6
> lib/test-parse-integer.c | 563 +++++++++++++++++++++++++++++++
> lib/vsprintf.c | 81 ++--
> mm/memcontrol.c | 19 -
> mm/memtest.c | 2
> mm/page_alloc.c | 2
> mm/shmem.c | 14
> 29 files changed, 1242 insertions(+), 635 deletions(-)
>
> So not counting lib/test-parse-integer.c, it's a net addition of 44
> lines. That's OK.
>
> My overall reaction to this is "oh god, not again". Is it really worth
> it?
I think giving good examples to people is always worth it :-)
> > +#define parse_integer(s, base, val) \
> > +({ \
> > + const char *_s = (s); \
> > + unsigned int _base = (base); \
> > + typeof(&(val)[0]) _val = (val); \
> > + \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), signed char *), \
> > + _parse_integer_sc(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), unsigned char *), \
> > + _parse_integer_uc(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), short *), \
> > + _parse_integer_s(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), unsigned short *), \
> > + _parse_integer_us(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), int *), \
> > + _parse_integer_i(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), unsigned int *), \
> > + _parse_integer_u(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), long *) && sizeof(long) == 4,\
> > + _parse_integer_i(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), long *) && sizeof(long) == 8,\
> > + _parse_integer_ll(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), unsigned long *) && sizeof(unsigned long) == 4,\
> > + _parse_integer_u(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), unsigned long *) && sizeof(unsigned long) == 8,\
> > + _parse_integer_ull(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), long long *), \
> > + _parse_integer_ll(_s, _base, (void *)_val), \
> > + __builtin_choose_expr( \
> > + __builtin_types_compatible_p(typeof(_val), unsigned long long *),\
> > + _parse_integer_ull(_s, _base, (void *)_val), \
> > + _parse_integer_link_time_error())))))))))))); \
> > +})
>
> Wow.
Yep, but blame the language not me.
Macro would be simpler with _Generic, but it is too early for that.
> > +/* internal, do not use */
> > +int _parse_integer_sc(const char *s, unsigned int base, signed char *val);
> > +int _parse_integer_uc(const char *s, unsigned int base, unsigned char *val);
> > +int _parse_integer_s(const char *s, unsigned int base, short *val);
> > +int _parse_integer_us(const char *s, unsigned int base, unsigned short *val);
> > +int _parse_integer_i(const char *s, unsigned int base, int *val);
> > +int _parse_integer_u(const char *s, unsigned int base, unsigned int *val);
> > +int _parse_integer_ll(const char *s, unsigned int base, long long *val);
> > +int _parse_integer_ull(const char *s, unsigned int base, unsigned long long *val);
>
> These all have fairly lengthy implementations. Could it all be done
> with a single function?
>
> int __parse_integer(const char *s, unsigned int base, unsigned int size, void *val);
>
> Where "size" is 1,2,4,8 with the top bit set if signed?
The question is why bother.
With smallish VM config I was testing, .text size difference is very small,
LOC-wise the difference doesn't exist as well (additional error checking adds
lines, not code per se). In the end _parse_integer() and simple_strto*() functions
will be removed as well.
With 4-arg dispatch function, every callsite will be more bloated:
simple_strto* (pointer, pointer, int)
parse_integer (pointer, int, pointer)
4-arg (pointer, int, int, pointer)
I think this code is way understandable than any mask-shift alternative:
int _parse_integer_sc(const char *s, unsigned int base, signed char *val)
{
long long tmp;
int rv;
rv = _parse_integer_ll(s, base, &tmp);
if (rv < 0)
return rv;
if (tmp != (signed char)tmp)
return -ERANGE;
*val = tmp;
return rv;
}
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