URL:
<http://savannah.gnu.org/bugs/?48371>
Summary: read(fd, NULL, 0) from /dev/klog blocks until there
is data
Project: The GNU Hurd
Submitted by: kon
Submitted on: Fri Jul 1 21:47:46 2016
Category: Hurd Servers
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: Standard Compliance
Status: None
Privacy: Public
Assigned to: None
Originator Name:
Originator Email:
Open/Closed: Open
Discussion Lock: Any
Reproducibility: None
Size (loc): None
Planned Release: None
Effort: 0.00
Wiki-like text discussion box:
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Details:
I patched rsyslog 8.16.0 to make it use /dev/klog on the Hurd. (Set
os_type="bsd" in configure.ac.) It opened /dev/klog all right but then hung
waiting for input. rpctrace showed that it was calling read with size=0.
This call is in plugins/imklog/bsd.c (klogWillRunPostPrivDrop). I removed the
call and rsyslog then started quickly.
The translator of /dev/klog is "/hurd/streamio kmsg". I assume storeio gets
to the dev_read function, which then waits for input from the kernel, without
noticing that the requested size is 0.
According to antrik, POSIX specifies that read with nbyte==0 must immediately
return 0 or return an error. This could be implemented in libc, libtrivfs, or
streamio. It seems best to implement this in streamio so that translators can
still return EBADF if the file was not opened for reading.
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