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Commit 79824820 authored by Akinobu Mita's avatar Akinobu Mita Committed by Linus Torvalds
Browse files

lib/string.c: introduce memchr_inv() 



memchr_inv() is mainly used to check whether the whole buffer is filled
with just a specified byte.

The function name and prototype are stolen from logfs and the
implementation is from SLUB.

Signed-off-by: default avatarAkinobu Mita <akinobu.mita@gmail.com>
Acked-by: default avatarChristoph Lameter <cl@linux-foundation.org>
Acked-by: default avatarPekka Enberg <penberg@kernel.org>
Cc: Matt Mackall <mpm@selenic.com>
Acked-by: default avatarJoern Engel <joern@logfs.org>
Cc: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 77311139

fs/logfs/logfs.h

+0 −1
Original line number Diff line number Diff line
@@ -618,7 +618,6 @@ static inline int logfs_buf_recover(struct logfs_area *area, u64 ofs, 
struct page *emergency_read_begin(struct address_space *mapping, pgoff_t index);

void emergency_read_end(struct page *page);

void logfs_crash_dump(struct super_block *sb);

void *memchr_inv(const void *s, int c, size_t n);

int logfs_statfs(struct dentry *dentry, struct kstatfs *stats);

int logfs_check_ds(struct logfs_disk_super *ds);

int logfs_write_sb(struct super_block *sb);

fs/logfs/super.c

+0 −22
Original line number Diff line number Diff line
@@ -90,28 +90,6 @@ void logfs_crash_dump(struct super_block *sb) 
	dump_segfile(sb);

}



/*

 * TODO: move to lib/string.c

 */

/**

 * memchr_inv - Find a character in an area of memory.

 * @s: The memory area

 * @c: The byte to search for

 * @n: The size of the area.

 *

 * returns the address of the first character other than @c, or %NULL

 * if the whole buffer contains just @c.

 */

void *memchr_inv(const void *s, int c, size_t n)

{

	const unsigned char *p = s;

	while (n-- != 0)

		if ((unsigned char)c != *p++)

			return (void *)(p - 1);



	return NULL;

}



/*

 * FIXME: There should be a reserve for root, similar to ext2.

 */

include/linux/string.h

+1 −0
Original line number Diff line number Diff line
@@ -114,6 +114,7 @@ extern int memcmp(const void *,const void *,__kernel_size_t); 
#ifndef __HAVE_ARCH_MEMCHR

extern void * memchr(const void *,int,__kernel_size_t);

#endif

void *memchr_inv(const void *s, int c, size_t n);



extern char *kstrdup(const char *s, gfp_t gfp);

extern char *kstrndup(const char *s, size_t len, gfp_t gfp);

lib/string.c

+54 −0
Original line number Diff line number Diff line
@@ -756,3 +756,57 @@ void *memchr(const void *s, int c, size_t n) 
}

EXPORT_SYMBOL(memchr);

#endif



static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes)

{

	while (bytes) {

		if (*start != value)

			return (void *)start;

		start++;

		bytes--;

	}

	return NULL;

}



/**

 * memchr_inv - Find an unmatching character in an area of memory.

 * @start: The memory area

 * @c: Find a character other than c

 * @bytes: The size of the area.

 *

 * returns the address of the first character other than @c, or %NULL

 * if the whole buffer contains just @c.

 */

void *memchr_inv(const void *start, int c, size_t bytes)

{

	u8 value = c;

	u64 value64;

	unsigned int words, prefix;



	if (bytes <= 16)

		return check_bytes8(start, value, bytes);



	value64 = value | value << 8 | value << 16 | value << 24;

	value64 = (value64 & 0xffffffff) | value64 << 32;

	prefix = 8 - ((unsigned long)start) % 8;



	if (prefix) {

		u8 *r = check_bytes8(start, value, prefix);

		if (r)

			return r;

		start += prefix;

		bytes -= prefix;

	}



	words = bytes / 8;



	while (words) {

		if (*(u64 *)start != value64)

			return check_bytes8(start, value, 8);

		start += 8;

		words--;

	}



	return check_bytes8(start, value, bytes % 8);

}

EXPORT_SYMBOL(memchr_inv);

mm/slub.c

+2 −45
Original line number Diff line number Diff line
@@ -655,49 +655,6 @@ static void init_object(struct kmem_cache *s, void *object, u8 val) 
		memset(p + s->objsize, val, s->inuse - s->objsize);

}



static u8 *check_bytes8(u8 *start, u8 value, unsigned int bytes)

{

	while (bytes) {

		if (*start != value)

			return start;

		start++;

		bytes--;

	}

	return NULL;

}



static u8 *check_bytes(u8 *start, u8 value, unsigned int bytes)

{

	u64 value64;

	unsigned int words, prefix;



	if (bytes <= 16)

		return check_bytes8(start, value, bytes);



	value64 = value | value << 8 | value << 16 | value << 24;

	value64 = (value64 & 0xffffffff) | value64 << 32;

	prefix = 8 - ((unsigned long)start) % 8;



	if (prefix) {

		u8 *r = check_bytes8(start, value, prefix);

		if (r)

			return r;

		start += prefix;

		bytes -= prefix;

	}



	words = bytes / 8;



	while (words) {

		if (*(u64 *)start != value64)

			return check_bytes8(start, value, 8);

		start += 8;

		words--;

	}



	return check_bytes8(start, value, bytes % 8);

}



static void restore_bytes(struct kmem_cache *s, char *message, u8 data,

						void *from, void *to)

{
@@ -712,7 +669,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, 
	u8 *fault;

	u8 *end;



	fault = check_bytes(start, value, bytes);

	fault = memchr_inv(start, value, bytes);

	if (!fault)

		return 1;
@@ -805,7 +762,7 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page) 
	if (!remainder)

		return 1;



	fault = check_bytes(end - remainder, POISON_INUSE, remainder);

	fault = memchr_inv(end - remainder, POISON_INUSE, remainder);

	if (!fault)

		return 1;

	while (end > fault && end[-1] == POISON_INUSE)