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Subject: Re: [PATCH 08/10] perf, tool: Add sysfs read file interface
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Jiri Olsa <jolsa@redhat.com>
Cc: acme@redhat.com, mingo@elte.hu, paulus@samba.org,
        cjashfor@linux.vnet.ibm.com, fweisbec@gmail.com, eranian@google.com,
        linux-kernel@vger.kernel.org
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Date: Wed, 04 Jul 2012 12:40:40 +0200
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On Wed, 2012-07-04 at 00:00 +0200, Jiri Olsa wrote:
> +int sysfs_read_file(const char *file, char *buf, size_t size)
> +{
> +       char path[PATH_MAX];
> +       FILE *fp;
> +       int ret = 0;
> +
> +       snprintf(path, PATH_MAX, "%s/%s", sysfs_mountpoint, file);
> +
> +       fp = fopen(path, "r");
> +       if (!fp)
> +               return -errno;
> +
> +       if (fread(buf, 1, size, fp) == 0)
> +               ret = -errno;
> +
> +       fclose(fp);
> +       return ret; 

Does sysfs guarantee a single read is complete? If not, we need a while
loop around that read until EOF or size.