Commit ff14417c authored Jun 25, 2015 by Rasmus Villemoes Committed by Linus Torvalds Jun 25, 2015

kernel/trace/blktrace.c: use strreplace() in do_blk_trace_setup()

Part of the disassembly of do_blk_trace_setup:

231b: e8 00 00 00 00 callq 2320 <do_blk_trace_setup+0x50>
231c: R_X86_64_PC32 strlen+0xfffffffffffffffc
2320: eb 0a jmp 232c <do_blk_trace_setup+0x5c>
2322: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
2328: 48 83 c3 01 add $0x1,%rbx
232c: 48 39 d8 cmp %rbx,%rax
232f: 76 47 jbe 2378 <do_blk_trace_setup+0xa8>
2331: 41 80 3c 1c 2f cmpb $0x2f,(%r12,%rbx,1)
2336: 75 f0 jne 2328 <do_blk_trace_setup+0x58>
2338: 41 c6 04 1c 5f movb $0x5f,(%r12,%rbx,1)
233d: 4c 89 e7 mov %r12,%rdi
2340: e8 00 00 00 00 callq 2345 <do_blk_trace_setup+0x75>
2341: R_X86_64_PC32 strlen+0xfffffffffffffffc
2345: eb e1 jmp 2328 <do_blk_trace_setup+0x58>

Yep, that's right: gcc isn't smart enough to realize that replacing '/' by
'_' cannot change the strlen(), so we call it again and again (at least
when a '/' is found). Even if gcc were that smart, this construction
would still loop over the string twice, once for the initial strlen() call
and then the open-coded loop.

Let's simply use strreplace() instead.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Liked-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1bb56471

kernel/trace/blktrace.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -439,7 +439,7 @@ int do_blk_trace_setup(struct request_queue q, char name, dev_t dev,
		{
		struct blk_trace old_bt, bt = NULL;
		struct dentry *dir = NULL;
		int ret, i;
		int ret;

		if (!buts->buf_size \|\| !buts->buf_nr)
		return -EINVAL;
		@@ -451,9 +451,7 @@ int do_blk_trace_setup(struct request_queue q, char name, dev_t dev,
		* some device names have larger paths - convert the slashes
		* to underscores for this to work as expected
		*/
		for (i = 0; i < strlen(buts->name); i++)
		if (buts->name[i] == '/')
		buts->name[i] = '_';
		strreplace(buts->name, '/', '_');

		bt = kzalloc(sizeof(*bt), GFP_KERNEL);
		if (!bt)

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