Messages in this thread Patch in this message | | | Date | Thu, 7 Feb 2013 16:06:20 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] fs/proc/vmcore.c: Put if tests in the top of the while loop to reduce duplication |
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On Sun, 03 Feb 2013 21:13:36 +0800 Zhang Yanfei <zhangyanfei.yes@gmail.com> wrote:
> From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> > > In function read_vmcore, two if tests are duplicate. Change the position > of them could reduce the duplication. This change does not affect > the behaviour of the function. >
hm, yes.
> --- a/fs/proc/vmcore.c > +++ b/fs/proc/vmcore.c > @@ -175,15 +175,16 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer, > start = map_offset_to_paddr(*fpos, &vmcore_list, &curr_m); > if (!curr_m) > return -EINVAL; > - if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen) > - tsz = buflen; > - > - /* Calculate left bytes in current memory segment. */ > - nr_bytes = (curr_m->size - (start - curr_m->paddr)); > - if (tsz > nr_bytes) > - tsz = nr_bytes; > > while (buflen) { > + if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen) > + tsz = buflen; > + > + /* Calculate left bytes in current memory segment. */ > + nr_bytes = (curr_m->size - (start - curr_m->paddr)); > + if (tsz > nr_bytes) > + tsz = nr_bytes; > + > tmp = read_from_oldmem(buffer, tsz, &start, 1); > if (tmp < 0) > return tmp; > @@ -198,12 +199,6 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer, > struct vmcore, list); > start = curr_m->paddr;
`start' gets changed here
> } > - if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen) > - tsz = buflen; > - /* Calculate left bytes in current memory segment. */ > - nr_bytes = (curr_m->size - (start - curr_m->paddr)); > - if (tsz > nr_bytes) > - tsz = nr_bytes;
So this code can calcualte a different value of `tsz'. But that won't get used. Looks right to me.
> } > return acc; > }
While we're there, let's squish that assignment-in-a-if pestilence and use max_t().
--- a/fs/proc/vmcore.c~fs-proc-vmcorec-put-if-tests-in-the-top-of-the-while-loop-to-reduce-duplication-fix +++ a/fs/proc/vmcore.c @@ -178,8 +178,7 @@ static ssize_t read_vmcore(struct file * return -EINVAL; while (buflen) { - if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen) - tsz = buflen; + tsz = max_t(size_t, buflen, PAGE_SIZE - (start & ~PAGE_MASK)); /* Calculate left bytes in current memory segment. */ nr_bytes = (curr_m->size - (start - curr_m->paddr)); _
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