Subject: bug#36455: closed (Re: bug#36455: Question on reading from socket(pair) instead from pipe)

From: [email-masked] (GNU bug Tracking System)
Date: Thu, 04 Jul 2019 06:49:02 +0000

Your bug report

#36455: Question on reading from socket(pair) instead from pipe

which was filed against the grep package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
36455: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=36455
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: bug#36455: Question on reading from socket(pair) instead from pipe
From: Paul Eggert <[email-masked]>
To: "Dr. Werner Fink" <[email-masked]>
Cc: [email-masked]
Date: Wed, 3 Jul 2019 23:47:50 -0700
List-Id: <debbugs-submit.debbugs.gnu.org>

Right, closing the bug report.

Subject: Question on reading from socket(pair) instead from pipe
From: "Dr. Werner Fink" <[email-masked]>
To: [email-masked]
Date: Mon, 1 Jul 2019 08:22:36 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

Hi,

with grep 3.3 I see for a FIFO this

  echo XXX | strace grep -E XXX
  [...]
  fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0xc), ...}) = 0
  stat("/dev/null", {st_mode=S_IFCHR|0666, st_rdev=makedev(0x1, 0x3), ...}) = 0
  fstat(0, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
  lseek(0, 0, SEEK_CUR)                   = -1 ESPIPE (Illegal seek)
  read(0, "XXX\n", 98304)                 = 4
  fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0xc), ...}) = 0
  write(1, "XXX\n", 4XXX)                    = 4
  read(0, "", 98304)                      = 0
  close(1)                                = 0
  close(2)                                = 0
  exit_group(0)                           = ?
  +++ exited with 0 +++

prefect but with libpipeline configured to use much faster socketpairs I see
this:

  strace -f ./mgrep -e XXX
  clone(strace: Process 2020 attached
  child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fb632fb4a10) = 2020
  [...]
  [pid  2020] execve("/usr/bin/grep", ["grep", "-e XXX"], 0x7ffd31f42ea8 /* 128 vars */ <unfinished ...>
  [...]
  [pid  2020] fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0xc), ...}) = 0
  [pid  2020] stat("/dev/null", {st_mode=S_IFCHR|0666, st_rdev=makedev(0x1, 0x3), ...}) = 0
  [pid  2020] fstat(0, {st_mode=S_IFSOCK|0400, st_size=0, ...}) = 0
  [pid  2020] lseek(0, 0, SEEK_CUR)       = -1 ESPIPE (Illegal seek)
  [pid  2020] read(0, "XXX\n", 98304)     = 4
  [pid  2020] read(0, "", 98304)          = 0
  [pid  2020] close(1)                    = 0
  [pid  2020] close(2)                    = 0
  [pid  2020] exit_group(1)               = ?
  [pid  2020] +++ exited with 1 +++

IMHO reading data from a FIFO/pipe or from a FSOCK/socket(pair) should result
in the same result.  The mgrep is a simple test C code which uses libpipeline
to write "XXX\n" to a FILE stream used on the input fd of the sub process for
the grep command:

  FILE *xy;
  int fd = dup(1);
  pipeline *p = pipeline_new();
  pipeline_want_in(p, -1);
  pipeline_want_out(p, fd);
  pipecmd *grep = pipecmd_new("/usr/bin/grep");
  [... handle options and arguments ...]
  xy = pipeline_get_infile (p);
  fprintf(xy, "XXX\n");
  fflush(xy);
  fclose(xy);

Nevertheless in both cases stdout for grep is 136/12 aka /dev/pts/12

Werner

-- 
  "Having a smoking section in a restaurant is like having
          a peeing section in a swimming pool." -- Edward Burr