From ff14417c0a00c9a906b4ba79fbecb79bd2435207 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Thu, 25 Jun 2015 15:02:28 -0700 Subject: [PATCH] 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 231c: R_X86_64_PC32 strlen+0xfffffffffffffffc 2320: eb 0a jmp 232c 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 2331: 41 80 3c 1c 2f cmpb $0x2f,(%r12,%rbx,1) 2336: 75 f0 jne 2328 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 2341: R_X86_64_PC32 strlen+0xfffffffffffffffc 2345: eb e1 jmp 2328 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 Acked-by: Steven Rostedt Liked-by: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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) -- 2.11.0