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Re: Bug#591386: since: Does not work as expected on GNU/Hurd

From: Emilio Pozuelo Monfort
Subject: Re: Bug#591386: since: Does not work as expected on GNU/Hurd
Date: Mon, 20 Sep 2010 21:20:06 -0000
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100619 Icedove/3.0.5


On 02/08/10 14:10, Axel Beckert wrote:
> "since" does not work as expected on GNU/Hurd (e.g. strauss):
> !57 Z47 ?127 L1 abe@strauss:ttyp0 (-zsh) 11:06:02 [~/debian/since-1.1] > 
> ./since /tmp/since-test
> foo
> !58 Z48 ?0 L1 abe@strauss:ttyp0 (-zsh) 11:06:25 [~/debian/since-1.1] > echo 
> bar >> /tmp/since-test
> !59 Z49 ?0 L1 abe@strauss:ttyp0 (-zsh) 11:06:32 [~/debian/since-1.1] > 
> ./since /tmp/since-test
> foo
> bar
> !60 Z50 ?0 L1 abe@strauss:ttyp0 (-zsh) 11:06:36 [~/debian/since-1.1] > 
> ./since /tmp/since-test
> foo
> bar
> !61 Z51 ?0 L1 abe@strauss:ttyp0 (-zsh) 11:08:07 [~/debian/since-1.1] > 
> ./since /tmp/since-test
> foo
> bar
> !62 Z52 ?0 L1 abe@strauss:ttyp0 (-zsh) 11:08:34 [~/debian/since-1.1] > cat 
> ~/.since
> 00023dea00000003:0000000400000000:0000000400000000
> 00023dea00000003:0000000800000000:0000000400000000
> 00023dea00000003:0000000800000000:0000000400000000
> 00023dea00000003:0000000800000000:0000000400000000
> Except for the data, ~/.since doesn't look different than on my
> laptop. There it also works as it should:

.since is actually wrong. The problem is the format string, it's
%016llx:%016llx:%016llx, but that's not correct on Hurd (due to the size of
dev_t). Adding a printf with the string format not in a variable, so gcc can
check it at compile time and emit warnings, like this:

      printf ("format: %s, 1: %016llx, 2: %016llx, 3: %016llx\n",
              sn->s_fmt, df->d_dev, df->d_ino, df->d_pos);

right before the "result = snprintf() call on line ~1500 emits:

-DDEBUG -g -o since since.c
since.c: In function ‘update_state_file’:
since.c:1499: warning: format ‘%016llx’ expects type ‘long long unsigned int’,
but argument 3 has type ‘dev_t’

Hardcoding the format string on the "result = snprintf()" call to
"%016x:%016llx:%016llx" makes .since correct:


(note the last number is (I guess) the position inside the file, so
0000000400000000 doesn't make sense for a file containing "foo", but 4 does).

Hardcoding the correct format string on the parsing function, since works fine:

root@hurd:~/since/since-1.1$ echo foo > test
root@hurd:~/since/since-1.1$ ./since test
root@hurd:~/since/since-1.1$ ./since test
root@hurd:~/since/since-1.1$ echo bar >> test
root@hurd:~/since/since-1.1$ ./since test
root@hurd:~/since/since-1.1$ ./since test
root@hurd:~/since/since-1.1$ cat /root/.since

Looking at why the string format is incorrect, I've found that make_fmt_field()
(the function that creates the format string) is called for that argument with a
dev_t argument, while the st_dev member of struct stat is not of type dev_t, but
of __fsid_t. This seems to be a POSIX violation (because sizeof(__fsid_t) !=
sizeof(dev_t), so it would be a bug in Hurd and not in since.

@Other Hurd porters: is my analysis correct?


P.S.: JFYI the PATH_MAX patch is more a workaround than a fix... the good fix
would be to stop using PATH_MAX and use dynamic allocation instead (in case you
want to fix it properly) though it's not high prio since long filename probably
don't work due to other issues in Hurd.

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