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e28fbd787c
Because I actually managed to hit deadlock in libvirt's child process due to glibc's mutex use in user database lookup, I figured it is worth documenting the issue for others to be aware of when writing a privileged multithreaded parent app that spawns child processes owned by non-privileged ids. * doc/glibc-functions/initgroups.texi (initgroups): Mention multithread safety. * doc/posix-functions/getpwuid.texi (getpwuid): Likewise. * doc/posix-functions/getpwuid_r.texi (getpwuid_r): Likewise. * doc/glibc-functions/getgrouplist.texi (getgrouplist): Mention getugroups. * doc/posix-functions/getgroups.texi (getgroups): Mention multithread safety and mgetgroups. Signed-off-by: Eric Blake <eblake@redhat.com>
40 lines
1.2 KiB
Plaintext
40 lines
1.2 KiB
Plaintext
@node getgroups
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@section @code{getgroups}
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@findex getgroups
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POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/getgroups.html}
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Gnulib module: getgroups
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Portability problems fixed by Gnulib:
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@itemize
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@item
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This function is missing on some platforms:
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mingw, MSVC 9.
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@item
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On some platforms, this function fails to reject a negative count,
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even though that is less than the size that would be returned:
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FreeBSD 7.2.
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@item
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On Ultrix 4.3, @code{getgroups (0, NULL)} always fails. See macro
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@samp{AC_FUNC_GETGROUPS}.
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@item
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On very old systems, this function operated on an array of @samp{int},
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even though that was a different size than an array of @samp{gid_t}.
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@end itemize
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Portability problems not fixed by Gnulib:
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@itemize
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@item
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This function is unsafe to call between @code{fork} and @code{exec} if
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the parent process is multi-threaded.
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@item
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It is unspecified whether the effective group id will be included in
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the returned list, nor whether the list will be sorted in any
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particular order. For that matter, some platforms include the
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effective group id twice, if it is also a member of the current
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supplemental group ids.
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@end itemize
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The Gnulib module @code{mgetgroups} provides a similar API.
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