lkml.org 
[lkml]   [2009]   [Sep]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectQuestion: how to handle too big f_pos Re: [PATCH] devmem: handle partial kmem write/read
I'm writing a patch against /dev/kmem...I found a problem.

/dev/kmem (and /proc/<pid>/mem) puts virtual addres to f->f_pos.

And, f->f_pos is loff_t .... signed value (not unsigned)

Then, this check
rw_verify_area(READ, file, pos, count);
=>
pos = *ppos;
if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
return retval;

always returns -EINVAL when I read /dev/kmem's valid address.

Then, how should I do for read /dev/kmem ? Any idea ?
(Added Al Viro to CC:)

What I'm really afraid of is /proc/<pid>/mem. IIUC, it's used by gdb to snoop
memory, (for example, at gcore).
I think gdb uses ptrace if it fails to read /proc/<pid>/mem but...it's deadly
slow.

Thanks,
-Kame

p.s. no problems in /proc/kcore..its offset is not bare addresss.





On Mon, 14 Sep 2009 11:29:01 +0800
Wu Fengguang <fengguang.wu@intel.com> wrote:

> Current vwrite silently ignores vwrite() to vmap holes.
> Better behavior should be stop the write and return
> on such holes.
>
> Also return on partial read, which may happen in future
> (eg. hit hwpoison pages).
>
> CC: Andi Kleen <andi@firstfloor.org>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> drivers/char/mem.c | 30 ++++++++++++++++++------------
> 1 file changed, 18 insertions(+), 12 deletions(-)
>
> --- linux-mm.orig/drivers/char/mem.c 2009-09-14 10:59:50.000000000 +0800
> +++ linux-mm/drivers/char/mem.c 2009-09-14 11:06:25.000000000 +0800
> @@ -444,18 +444,22 @@ static ssize_t read_kmem(struct file *fi
> if (!kbuf)
> return -ENOMEM;
> while (count > 0) {
> + unsigned long n;
> +
> sz = size_inside_page(p, count);
> - sz = vread(kbuf, (char *)p, sz);
> - if (!sz)
> + n = vread(kbuf, (char *)p, sz);
> + if (!n)
> break;
> - if (copy_to_user(buf, kbuf, sz)) {
> + if (copy_to_user(buf, kbuf, n)) {
> free_page((unsigned long)kbuf);
> return -EFAULT;
> }
> - count -= sz;
> - buf += sz;
> - read += sz;
> - p += sz;
> + count -= n;
> + buf += n;
> + read += n;
> + p += n;
> + if (n < sz)
> + break;
> }
> free_page((unsigned long)kbuf);
> }
> @@ -551,11 +555,13 @@ static ssize_t write_kmem(struct file *
> free_page((unsigned long)kbuf);
> return -EFAULT;
> }
> - sz = vwrite(kbuf, (char *)p, sz);
> - count -= sz;
> - buf += sz;
> - virtr += sz;
> - p += sz;
> + n = vwrite(kbuf, (char *)p, sz);
> + count -= n;
> + buf += n;
> + virtr += n;
> + p += n;
> + if (n < sz)
> + break;
> }
> free_page((unsigned long)kbuf);
> }
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>



\
 
 \ /
  Last update: 2009-09-15 10:03    [W:0.151 / U:0.176 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site