Messages in this thread Patch in this message |  | | From | Rasmus Villemoes <> | Subject | [PATCH v2 3/8] blktrace: use strreplace in do_blk_trace_setup | Date | Tue, 9 Jun 2015 01:26:51 +0200 |
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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> --- v2: same patch, added Ack.
kernel/trace/blktrace.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 483cecfa5c17..4eeae4674b5a 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -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) -- 2.1.3
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