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Re: [Help-tar] Does GNU tar close its input pipe before seeing EOF on it
Re: [Help-tar] Does GNU tar close its input pipe before seeing EOF on it?
Tue, 2 Mar 2010 13:49:36 +0100 (CET)
On Mon, 1 Mar 2010, Sergey Poznyakoff wrote:
Ersek, Laszlo <address@hidden> ha escrit:
Does GNU tar (and if so, under what circumstances) close its input
pipe before seeing EOF on it?
Yes, it does. The input stream is closed if tar determines that
there is nothing more to be read from there (e.g. it has received
the two null blocks that end the archive or has extracted all
From the tar-1.22.91 alpha release (and I apologize if it's obsolete or
irrelevant for this discussion), "src/system.c", sys_wait_for_child():
173 if (WIFSIGNALED (wait_status))
175 int sig = WTERMSIG (wait_status);
176 if (!(!eof && sig == SIGPIPE))
177 FATAL_ERROR ((0, 0, _("Child died with signal %d"), sig));
179 else if (WEXITSTATUS (wait_status) != 0)
180 FATAL_ERROR ((0, 0, _("Child returned status %d"),
181 WEXITSTATUS (wait_status)));
It seems that tar considers it okay when its child filter dies with
SIGPIPE *if* tar has not yet seen an EOF on the pipe. I guess the
motivation is to accept a SIGPIPE in response to tar closing the pipe
Consider a filter encountering a genuine error. The filter intends to
print an error message to stderr, then exit with a non-zero exit status.
Suppose the filter is killed with SIGPIPE when it tries to print the error
message, because its STDERR_FILENO refers to a pipe (or socket) that is
broken. What will tar do?
Do we trust tar to notice the problem by detecting the incomplete tar
stream and/or the bad checksum? What if the filter produces a stream
carrying multiple concatenated tar files (suppose tar was started with the
appropriate options), and the problem occurs in the filter at the boundary
between the two tar files?
Another case is when the filter does not encounter an error, but simply
tries to produce a great amount of diagnostic output (like some verbose
progress report or debug trace), and its stderr pipe is broken.
In short, can tar be sufficiently certain that any SIGPIPE returned for
the child, before tar meets EOF on the pipe, is due to tar closing the
Thank you very much,