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From: "Mikhail T." <mi+thun@aldan.algebra.com>
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To: Kostik Belousov <kostikbel@gmail.com>
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Cc: stable@FreeBSD.org
Subject: Re: Can close-ing a pipe trigger a SIGPIPE?
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Kostik Belousov ΞΑΠΙΣΑΧ(ΜΑ):
> Take ktrace of both parent and child.
>   
I can see the curious piece right here:

The child exits:

 92723 tclsh8.5 CALL  exit(0)

The parent masks SIGPIPE (as part of my workaround):

 92722 tclsh8.5 CALL  sigaction(SIGPIPE,0x7fffffffa9e0,0)
 92722 tclsh8.5 RET   sigaction 0

This 0-size write must be part of the pipe-closing -- descriptors 4 and
5 must be the pipe's:

 92722 tclsh8.5 CALL  write(0x4,0x800e24028,0)
 92722 tclsh8.5 RET   write -1 errno 32 Broken pipe
 92722 tclsh8.5 PSIG  SIGPIPE caught handler=0x800f126d0 mask=0x0 code=0x0
 92722 tclsh8.5 CALL  sigreturn(0x7fffffffa0c0)
 92722 tclsh8.5 RET   sigreturn JUSTRETURN
 92722 tclsh8.5 CALL  close(0x5)
 92722 tclsh8.5 RET   close 0
 92722 tclsh8.5 CALL  close(0x4)
 92722 tclsh8.5 RET   close 0

Why would it write 0 bytes? Is doing so triggering a SIGPIPE now -- but,
perhaps, didn't use to?

Thanks!

    -mi