Re: [LTP] [PATCH 1/1] openposix_mmap_11_4

[naresh kamboju <naresh.kernel@gmail.com>]

Hi Fan,

please give your comments on this issue.

It is glibc and kernel issue discussions.

http://bugs.gentoo.org/197191

Is this info is up to the date?

 http://www.opengroup.org/onlinepubs/009695399/functions/mmap.html

I did not find mmap (3) in kernel man pages.

http://www.kernel.org/doc/man-pages/online/dir_section_3.html

I am not sure about glibc mmap implementation.

http://sources.redhat.com/cgi-bin/cvsweb.cgi/?cvsroot=glibc

if you find any info.
please share.

Best regards,
Naresh Kamboju

On Fri, Aug 7, 2009 at 6:11 PM, Subrata Modak<subrata@linux.vnet.ibm.com> wrote:
> On Thu, 2009-08-06 at 21:39 +0530, naresh kamboju wrote:
>> Hi,
>>
>> In addition to the below Link discussion
>>
>> Date: 16 Jul 2009
>> http://www.mail-archive.com/ltp-list@lists.sourceforge.net/msg07506.html
>>
>> patch is not yet committed to LTP CVs.
>
> I am a bit perplexed by all these links. Can you please RESEND the
> concerned patch with the required description. I would then check that
> in.
>
> Regards--
> Subrata
>
>>
>> as per test case Description
>>
>> /*****************************************************/
>>  * Implementation performs mapping operations over whole pages.
>>  * Thus, while the argument len
>>  * need not meet a size or alignment constraint,
>>  * the implementation shall include, in any mapping
>>  * operation, any partial page specified by the range [pa,pa+len).
>>  * The system shall always zero-fill any partial page at the end of an object.
>>  * Further, the system shall never write out any modified portions of
>>  * the last page of an object which are beyond its end.
>>  *
>>  * Test step:
>>  * 1. Create a process, in this process:
>>       a. map a file  with size of 1/2 * page_size,
>>  *       set len = 1/2 * page_size
>>  *    b. Read the partial page beyond the object size.
>>  *       Make sure the partial page is zero-filled;
>>  *    c. Modify a byte in the partial page, then un-map the and close the
>>  *       file descriptor.
>>  * 2. Wait for the child proces to exit, then
>>  *    Map the file again,
>>  *    read the byte from the position modified at step 1-c and check.
>>  */
>> /****************************************************/
>>
>> please note the below discussion
>>
>> http://bugs.gentoo.org/197191
>>
>> Ref:
>> http://www.opengroup.org/onlinepubs/009695399/functions/mmap.html
>>
>> fan he,
>>
>> please make sure who is going to do this is it coming from kernel or glibc?
>>
>> Best regards
>> Naresh Kamboju
>>
>>
>> >On Mon, 2009-07-20 at 00:46 -0700, Garrett Cooper wrote:
>> > On Sun, Jul 19, 2009 at 10:54 PM, Michal
>> > Simek<michal.si...@petalogix.com> wrote:
>> > > Hi,
>> > >> On Sat, 2009-07-18 at 12:28 -0700, Garrett Cooper wrote:
>> > >>
>> > >>> On Thu, Jul 16, 2009 at 11:37 PM, hefan<f...@novell.com> wrote:
>> > >>>
>> > >>>> hi,
>> > >>>>
>> > >>>> *[Patch 1/1] Patch for fixing the failed testcase openposix_mmap_11_4
>> > >>>>
>> > >>>> -modified the file
>> > >>>> *testcases/open_posix_testsuite/conformance/interfaces/mmap/11-4.c
>> > >
>> > > First of all - this is really small explanation why you are fixing this
>> > > issue. After some month
>> > > none will know why you did this change.
>> > >
>> > >
>> > >>>>
>> > >>>> Signed-off-by:  fredrick he <f...@novell.com>
>> > >>>>
>> > >>>> ---
>> > >>>> ltp.orig/testcases/open_posix_testsuite/conformance/interfaces/mmap/11-4.c
>> > >>>>       2009-07-17 11:53:36.000000000 +0800
>> > >>>> +++
>> > >>>> ltp/testcases/open_posix_testsuite/conformance/interfaces/mmap/11-4.c
>> > >>>> 2009-07-17 11:57:09.000000000 +0800
>> > >>>> @@ -130,7 +130,9 @@ int main()
>> > >>>>   flag = MAP_SHARED;
>> > >>>>   off = 0;
>> > >>>>   pa = mmap(addr, len, prot, flag, fd_2, off);
>> > >>>> -  pa_2 = mmap(addr, len, prot, flag, fd_2, off);
>> > >>>> +  addr = pa;
>> > >>>> +  memset(addr,0,len*2);
>> > >>>> +  pa_2 = mmap(addr, len, prot, flag|MAP_FIXED, fd_2, off);
>> > >>>>   if (pa_2 == MAP_FAILED)
>> > >>>>   {
>> > >>>>     printf("Test FAIL: " TNAME " Error at 2nd mmap(): %s\n",
>> > >>>>
>> > >>> Hi Fan,
>> > >>>     Some questions / observations:
>> > >>>
>> > >>> 1. Yes, the testcases does fail on my machine today.
>> > >>> 2. Yes, doing what you say above does work (at least the testcase passes).
>> > >>> 3. Are you positive that your set of steps above in fact don't
>> > >>> invalidate the purpose of the testcase, by accident, in particular the
>> > >>> memset call? I ask because of the following statement in the mmap
>> > >>> manpage:
>> > >>>
>> > >>>        If addr is NULL, then the kernel chooses the address at which to
>> > >>> create
>> > >>>        the mapping; this is the most portable method of creating  a  new
>> > >>> map-
>> > >>>        ping.   If  addr  is not NULL, then the kernel takes it as a hint
>> > >>> about
>> > >>>        where to place the mapping; on Linux, the mapping will be created
>> > >>> at  a
>> > >>>        nearby  page  boundary.   The address of the new mapping is
>> > >>> returned as
>> > >>>        the result of the call.
>> > >>>
>> > >>> What you're in effect doing is changing the 2nd mmap call from an
>> > >>> arbitrary address to a set virtual address at 0x0. Is that indeed
>> > >>> correct?
>> > >>>
>> > >> in this case, the situation is like this, we create a new file about 512
>> > >> bytes and mmap it into the mem, then we modify one byte besides the 512
>> > >> bytes address, and munmap it. and in the father process remmap it back
>> > >> to check whether the one more byte is write back to the files.
>> >
>> > Ok.
>> >
>> > >> i have checked that when finished munmap and close the file in the child
>> > >> process, the file didn't contain the 513th byte, the size of this file
>> > >> is right 512 bytes.but in this case after the second mmap finished, the
>> > >> 513th byte does appear again. it's a conflict.
>> > >>
>> > >> in my opinion this is because of the compiler or some optimizations. so
>> > >> i think the memory should to be memset before mmap and it does work.
>> >
>> > No, according to the manpage it'll map to the boundary of the closest
>> > page size, in my opinion what might be occurring is the system is
>> > either overallocating or underallocating, depending on the system page
>> > size and what's being passed in for a length. What the page size is,
>> > I'd surely like to know...
>> here in my environment the page size is 1024 got by using
>> sysconf(_SC_PAGE_SIZE) in this testcase
>> >
>> > > If is the problem with compiler/optimization means that tests is ok -
>> > > the problem is with your
>> > > compiler not with code.
>> > > This need more investigations to find out where the problem is.
>> >
>> > I wouldn't necessarily say that. Based on Frederick's explanation, it
>> > sounds like someone fed in an inappropriate bound, or didn't NUL
>> > terminate the boundary and just went off into uncharted territory
>> > without first checking where they were `on the map'.
>> >
>> > Based on my experience and recollection, this is legitimate in C
>> > behavior as long as you're within the applications memory limits --
>> > you've just entered the twilight zone between realities, where you're
>> > beyond your address space, but not beyond the point of no return
>> > (EACCES), where the kernel *should* terminate your userland app.
>> >yeah, that's the keypoint. but it doesn't terminate our userland app.
>>
>> >i mean that here is a mistake on the way this testcase check the result.
>> >ideally, the mmap should only use half a page and it has no
>> >resposibility on the rest of the page, so we shouldn't judge the mmap by
>> >the rest of the page which is none of business with mmap.
>>
>> >so if we suppose that the mmap does affect the rest of the page(  is it
>> >the purpose to design this testcase ? ), we should make sure that this
>> >area has been clear before we mmap the file into this area. that's why i
>> >use memset and flag MAP_FIXED.
>>
>> >
>> > Whether or not that was the intention of the POSIX folks, is another
>> > question indeed, as the documentation states (in the header of the .c
>> > file):
>> >
>> >  * Implementation performs mapping operations over whole pages.
>> >  * Thus, while the argument len
>> >  * need not meet a size or alignment constraint,
>> >  * the implementation shall include, in any mapping
>> >  * operation, any partial page specified by the range [pa,pa+len).
>> >  * The system shall always zero-fill any partial page at the end of an object.
>> >  * Further, the system shall never write out any modified portions of
>> >  * the last page of an object which are beyond its end.
>> >
>> > So unless they're completely misinterpreting the meaning of mmap, it
>> > sounds like there's a bug in a number of `POSIX-compliant' operating
>> > systems that needs to be resolved (FreeBSD and Linux included).
>> >
>> > However, before jumping to conclusions, I think that it's prudent to
>> > narrow down where and why this is occurring...
>> >
>> > >>> 4. Have you talked to the openposix test suite folks about this yet?
>> > >>>
>> > >> no,i have no idea on how to talk to the openposix and i do want to talk
>> > >> to them :) can you give me some suggestions about this? thx~
>> >
>> > The project administrators are available, as noted, here:
>> >
>> > https://sourceforge.net/project/memberlist.php?group_id=64592
>> >
>> > Thanks,
>> > -Garrett
>
>

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