linux-kernel - Re: fanotify: fix support of large files

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Date:	Thu, 11 Jul 2013 15:10:35 -0700
From:	Justin Maggard <jmaggard10@...il.com>
To:	Heinrich Schuchardt <xypron.glpk@....de>
Cc:	linux-kernel@...r.kernel.org, eparis@...hat.com,
	LinoSanfilippo@....de, Tzvetan Chaliavski <tzvetanc@...mtouch.com>
Subject: Re: fanotify: fix support of large files

On Mon, Apr 22, 2013 at 11:49 AM, Heinrich Schuchardt
<xypron.glpk@....de> wrote:
>
> Hello Justin,
>
> I downloaded the example,
> http://www.lanedo.com/~aleksander/fanotify/fanotify-example.c
> compiled it without modification
> $ gcc fanotify-example.c -o fanotify-example
> and started the executable. In a separate windows I executed
> truncate -s 2048m 2048m
>
> This is the output of the first window:
> $ sudo ./fanotify-example /home/user/temp/
> Started monitoring directory '/home/user/temp/'...
> Received event in path '/home/user/temp/2048m' pid=3659 (truncate):
>         FAN_OPEN
> Received event in path '/home/user/temp/2048m' pid=3659 (truncate):
>         FAN_CLOSE_WRITE
>
> $ uname -a
> Linux family2 3.8.0 #1 SMP Fri Feb 22 22:07:58 CET 2013 i686 GNU/Linux
>

Ah yes, that's the reason.  I'm running on x86_64.  32-bit platforms
actually work if you set O_LARGEFILE.  From /usr/incude/bits/fcntl.h:

#ifdef __USE_LARGEFILE64
# if __WORDSIZE == 64
#  define O_LARGEFILE   0
# else
#  define O_LARGEFILE   0100000
# endif
#endif

If I include <asm/fcntl.h> instead of <fcntl.h>, it gets set to
0x8000, and my large file fanotify test works.  Or, of course, I can
define that flag locally and use it.  But it feels like I shouldn't
have to do that.

-Justin

>
> To reproduce your problem, could you, please, provide the Linux configuration file (look in your /boot directory) and a link to the source of the Linux kernel version you use. Then I can use your configuration file to compile that kernel version.
>
> Best regards
>
> Heinrich Schuchardt
>
>
> On 19.04.2013 21:23, Justin Maggard wrote:
>>
>> On Sat, Apr 13, 2013 at 4:54 AM, Heinrich Schuchardt<xypron.glpk@....de>  wrote:
>>>
>>> Dear Justin,
>>>
>>> looking at the example at
>>> http://www.lanedo.com/~aleksander/fanotify/fanotify-example.c
>>> the large file support is enabled by passing O_LARGEFILE to fanotify_init:
>>>
>>>    if ((fanotify_fd = fanotify_init (FAN_CLOEXEC,
>>>                                      O_RDONLY | O_CLOEXEC | O_LARGEFILE))<
>>> 0)
>>>
>>> Could you, please, check if this solves your issue.
>>>
>>> (I am resending this message because HTML was rejected by
>>> linux-kernel@...r.kernel.org).
>>>
>>> Best regards
>>>
>>> Heinrich Schuchardt
>>>
>>
>> No, unfortunately that doesn't help.  I slightly modifed
>> fanotify-example.c to call perror() when read() fails, and here's the
>> output:
>>
>> jmaggard@...ggard-W520:~/fanotify-test$ sudo ./fanotify-example .&
>> [1] 7248
>> jmaggard@...ggard-W520:~/fanotify-test$ Started monitoring directory '.'...
>> truncate -s 2047m 2047m
>> Received event in path '/home/jmaggard/fanotify-test/2047m' pid=7250 (unknown):
>> FAN_OPEN
>> FAN_CLOSE_WRITE
>> jmaggard@...ggard-W520:~/fanotify-test$ truncate -s 2048m 2048m
>> read: Value too large for defined data type
>>
>> -Justin
>>
>
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