Re: [PATCH] Sort module list - use ppos instead of m->private

Mathieu Desnoyers
2007-08-25T00:10:27Z

* Andrew Morton (akpm@linux-foundation.org) wrote:
> On Fri, 24 Aug 2007 11:39:33 -0400
> Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:
>
> > Sort modules list - use ppos instead of m->private
> >
> > When reading the data by small chunks (i.e. byte by byte), the index (ppos) is
> > incremented by seq_read() directly and no "next" callback is called when going
> > to the next module.
> >
> > Therefore, use ppos instead of m->private to deal with the fact that this index
> > is incremented directly to pass to the next module in seq_read() after the
> > buffer has been emptied.
>
> Confused. What problem is this patch fixing? I'm guessing that something
> is going wrong when /proc/modules is read one-byte-at-a-time?
>
> <tests that>
>
> <nope>
>
> Better changelogs, please.
>

Ok, will append this in the changelog (I sent this to Rusty earlier
today):

Small test program for this:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define BUFSIZE 1024

int main()
{
int fd = open("/proc/modules", O_RDONLY);
char buf[BUFSIZE];
ssize_t size;

do {
size = read(fd, buf, 1);
printf("%c", buf[0]);
usleep(100000);
} while(size > 0);

close(fd);
return 0;
}

Before fix, it prints the first module indefinitely. The patch fixes
this.

I will also append more detail to "Sort module list by pointer address
to get coherent sleepable seq_file iterators" changelog before the
2.6.23-rc3-mm1 repost.

Mathieu