From: "Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>,
Cyril Hrubis <chrubis-AlSwsSmVLrQ@public.gmane.org>
Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH] ioctl_list.2: BLKRASET/BLKRAGET take unsigned long
Date: Mon, 10 Apr 2017 17:21:34 +0200 [thread overview]
Message-ID: <f421cf72-791c-ba59-42d4-4dcef9a71b04@gmail.com> (raw)
In-Reply-To: <CAK8P3a0KzhqFZqvPH4q7_Nb6+TMmhCWXDi_-wQG=mi-1U=Ccxw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On 02/15/2017 01:04 PM, Arnd Bergmann wrote:
> On Wed, Feb 15, 2017 at 12:22 PM, Cyril Hrubis <chrubis-AlSwsSmVLrQ@public.gmane.org> wrote:
>> [CCing linux api as well]
>>> The BLKRASET/BLKRAGET ioctls() take unsigned long, if I pass int * to
>>> the BLKRAGET ioctl on x86_64 (or on any other arch where sizeof(int) !=
>>> sizeof(long)) the BLKRAGET ioctl will rewrite four bytes on the stack.
>>>
>>> If you look at block/ioctl.c in kernel sources you can clearly see that
>>> BLKRAGET ioctl calls put_long().
>
> BLKFRAGET as well, fwiw, see compat_blkdev_ioctl().
> We might as well include them in the list.
>
>>> I also wonder if it's OK to pass int value to ioctl() at all, the arg
>>> value seems to be unsigned long in the syscall definition in fs/ioctl.c
>>> and there does not seem to be any glibc magic around the syscall.
>
> This shouldn't matter, if you pass an 'int' into a function that takes
> a 'long', it will be extended if necessary. The question is more about
> how it gets interpreted, and in this case it's done by assigning to
>
> struct backing_dev_info {
> ...
> unsigned long ra_pages; /* max readahead in PAGE_SIZE units */
> ...
> };
>
> Large values will not be used in practice (these are capped by the
> I/O sizes), but I guess you can set a value larger than UINT_MAX
> and read it back later.
>
>>> man2/ioctl_list.2 | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/man2/ioctl_list.2 b/man2/ioctl_list.2
>>> index 0165c77..c8efd66 100644
>>> --- a/man2/ioctl_list.2
>>> +++ b/man2/ioctl_list.2
>>> @@ -311,8 +311,8 @@ l l l l.
>>> 0x0000125F BLKRRPART void
>>> 0x00001260 BLKGETSIZE unsigned long *
>>> 0x00001261 BLKFLSBUF void
>>> -0x00001262 BLKRASET int
>>> -0x00001263 BLKRAGET int *
>>> +0x00001262 BLKRASET unsigned long
>>> +0x00001263 BLKRAGET unsigned long *
>>> 0x00000001 FIBMAP int * // I-O
>>> 0x00000002 FIGETBSZ int *
>>> 0x80086601 FS_IOC_GETFLAGS int *
>
> Looks correct to me.
Thanks for reviewing this, Arnd.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2017-04-10 15:21 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-15 11:20 [PATCH] ioctl_list.2: BLKRASET/BLKRAGET take unsigned long Cyril Hrubis
[not found] ` <20170215112015.GA27080-2UyX9mZUyMU@public.gmane.org>
2017-02-15 11:22 ` Cyril Hrubis
[not found] ` <20170215112205.GA27269-2UyX9mZUyMU@public.gmane.org>
2017-02-15 12:04 ` Arnd Bergmann
[not found] ` <CAK8P3a0KzhqFZqvPH4q7_Nb6+TMmhCWXDi_-wQG=mi-1U=Ccxw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-15 12:59 ` Cyril Hrubis
[not found] ` <20170215125946.GA27511-2UyX9mZUyMU@public.gmane.org>
2017-02-15 14:29 ` Cyril Hrubis
2017-04-10 15:21 ` Michael Kerrisk (man-pages) [this message]
2017-03-14 13:21 ` Cyril Hrubis
[not found] ` <20170314132120.GA8347-2UyX9mZUyMU@public.gmane.org>
2017-04-03 14:02 ` Cyril Hrubis
2017-04-10 15:21 ` Michael Kerrisk (man-pages)
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