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Fixes:
lib/util/tfork.c:260:3: warning: Value stored to 'ret' is never read <--[clang]
Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Display a meaningful process title for the waiter process, now that smbd is
calling setproctitle_init() and this value will be displayed in ps
output.
Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Tue Sep 26 04:38:59 CEST 2017 on sn-devel-144
Make closing of the event_fd the global responsibility of the
parent process if it called tfork_event_fd().
Bug: https://bugzilla.samba.org/show_bug.cgi?id=13037
Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
The previous design relied on only calling close() of the status pipe.
We now write a single 0 byte to the status FD as well as closing it in the
parent process. Both of these operations typically trigger a read
event on the other end of the FD, held in the waiter process (the child).
The child process blocks on the status FD, until it becomes readable.
However if there is a sibling process that was launched after the waiter
process they also will hold the status FD open and the status FD would,
until this change, never become readable to the waiter process (the child).
This caused the waiter process (child) not to exit and the parent process
to hang in tfork_status() while expecting the waitpid() to return.
That is, file descriptors are essentially global variables copied
to children in the process tree. The last child that (unwittingly) holds
the file descriptor open is the one that needs to trigger the close() this
code previously depended on.
Without this change, there is no notification of process death until
all these unrelated children exit for their own reasons.
We can write up to 4K (PIPE_BUF) into this pipe before blocking,
but we only write one byte. Additionally sys_write() refuses to block.
Bug: https://bugzilla.samba.org/show_bug.cgi?id=13037
Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This function is a solution to the problem of fork() requiring special
preperations in the caller to handle SIGCHLD signals and to reap the
child by wait()ing for it.
Instead, tfork provides a pollable file descriptor. The caller gets the
file descriptor by calling tfork_event_fd() on the handle returned from
tfork_create() and the caller can then get the status of the child
with a call to tfork_status().
tfork avoids raising SIGCHLD signals in the caller by installing a
temporary SIGCHLD handler from inside tfork_create() and tfork_status().
The termination signal of other child processes not created with tfork()
is forwarded to the existing signal handler if any.
There's one thing this thing can't protect us against and that is if a
process installs a SIGCHLD handler from one thread while another thread
is running inside tfork_create() or tfork_status() and the signal
handler doesn't forward signals for exitted childs it didn't fork, ie
our childs.
Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Ralph Boehme <slow@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
triple-fork to avoid handling SIGCHLD in the parent.
This function is a workaround for the problem of using fork() in
library code. In that case the library should avoid setting a global
signal handler for SIGCHLD, because the application may wants to use its
own handler.
status_fd can be used to wait for the child to exit and get its exit
status.
Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
