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SubjectRe: [PATCH 0/2] (Was: perf_event_mmap(vma) && !vma->vm_mm)
On 10/17, Peter Zijlstra wrote:
>
> - name = arch_vma_name(vma);
> + name = (char *)arch_vma_name(vma);

Yes, this way we do not need another non-const ptr.

OK, please consider another cleanup on top of this change.

Just to "complete" the discussion, do not even bother to reply
if you think it doesn't make sense ;)

---
Subject: [PATCH] perf: Factor out strncpy() in perf_event_mmap_event()
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 17 Oct 2013 20:04:17 +0200

While this is really minor, but strncpy() does the unnecessary
zero-padding till the end of tmp[16] and it is called every time
we are going to use the string literal.

Turn these strncpy()'s into the single strlcpy() under the new
label, saves 72 bytes.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/events/core.c | 32 ++++++++++++++++----------------
1 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e7ace78..93ddf3d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5108,8 +5108,8 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)

buf = kmalloc(PATH_MAX, GFP_KERNEL);
if (!buf) {
- name = strncpy(tmp, "//enomem", sizeof(tmp));
- goto got_name;
+ name = "//enomem";
+ goto cpy_name;
}
/*
* d_path works from the end of the rb backwards, so we
@@ -5118,8 +5118,8 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
*/
name = d_path(&file->f_path, buf, PATH_MAX - sizeof(u64));
if (IS_ERR(name)) {
- name = strncpy(tmp, "//toolong", sizeof(tmp));
- goto got_name;
+ name = "//toolong";
+ goto cpy_name;
}
inode = file_inode(vma->vm_file);
dev = inode->i_sb->s_dev;
@@ -5127,30 +5127,30 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
gen = inode->i_generation;
maj = MAJOR(dev);
min = MINOR(dev);
-
+ goto got_name;
} else {
name = (char *)arch_vma_name(vma);
- if (name) {
- name = strncpy(tmp, name, sizeof(tmp) - 1);
- tmp[sizeof(tmp) - 1] = '\0';
- goto got_name;
- }
+ if (name)
+ goto cpy_name;

if (vma->vm_start <= vma->vm_mm->start_brk &&
vma->vm_end >= vma->vm_mm->brk) {
- name = strncpy(tmp, "[heap]", sizeof(tmp));
- goto got_name;
+ name = "[heap]";
+ goto cpy_name;
}
if (vma->vm_start <= vma->vm_mm->start_stack &&
vma->vm_end >= vma->vm_mm->start_stack) {
- name = strncpy(tmp, "[stack]", sizeof(tmp));
- goto got_name;
+ name = "[stack]";
+ goto cpy_name;
}

- name = strncpy(tmp, "//anon", sizeof(tmp));
- goto got_name;
+ name = "//anon";
+ goto cpy_name;
}

+cpy_name:
+ strlcpy(tmp, name, sizeof(tmp));
+ name = tmp;
got_name:
/*
* Since our buffer works in 8 byte units we need to align our string
--
1.5.5.1



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