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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2014-07-07 08:39:22 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2014-07-07 09:07:18 +0200 |
| commit | 8ab32b4785eaa4d4248b2e69fff89d4b6538929c (patch) | |
| tree | fc4837e52cdfeb7df5aa0c6921cb9a82a76f9926 | |
| parent | d3695ae2c75314b8cb043d35e2aad6085e4403c8 (diff) | |
epoll_ctl.2: BUGS: EPOLLWAKEUP is silently ignored without CAP_BLOCK_SUSPEND
If the caller does not have CAP_BLOCK_SUSPEND, then EPOLLWAKEUP
is silently ignored.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
| -rw-r--r-- | man2/epoll_ctl.2 | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/man2/epoll_ctl.2 b/man2/epoll_ctl.2 index 1db129d3b..84ad8436a 100644 --- a/man2/epoll_ctl.2 +++ b/man2/epoll_ctl.2 @@ -174,6 +174,7 @@ until the next call to on the same .BR epoll (7) file descriptor. +See also BUGS. .SH RETURN VALUE When successful, .BR epoll_ctl () @@ -270,6 +271,33 @@ when using Applications that need to be portable to kernels before 2.6.9 should specify a non-null pointer in .IR event . + +If +.B EPOLLWAKEUP +is specified in +.IR flags , +but the caller does not have the +.BR CAP_BLOCK_SUSPEND +capability, then the +.B EPOLLWAKEUP +flag is +.IR "silently ignored" . +This unfortunate behavior is necessary because no validity +checks were performed on the +.IR flags +argument in the original implementation, and the addition of the +.B EPOLLWAKEUP +with a check that caused the call to fail if the caller did not have the +.B CAP_BLOCK_SUSPEND +capability caused a breakage in at least one existing user-space +application that happened to randomly (and uselessly) specify this bit. +.\" commit a8159414d7e3af7233e7a5a82d1c5d85379bd75c (behavior change) +.\" https://lwn.net/Articles/520198/ +A robust application should therefore double check that it has the +.B CAP_BLOCK_SUSPEND +capability if attempting to use the +.B EPOLLWAKEUP +flag. .SH SEE ALSO .BR epoll_create (2), .BR epoll_wait (2), |