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path: root/include/linux/eventfd.h
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* eventfd - allow atomic read and waitqueue removeDavide Libenzi2010-01-25
| | | | | | | | | | | | KVM needs a wait to atomically remove themselves from the eventfd ->poll() wait queue head, in order to handle correctly their IRQfd deassign operation. This patch introduces such API, plus a way to read an eventfd from its context. Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Avi Kivity <avi@redhat.com>
* anonfd: split interface into file creation and installDavide Libenzi2009-09-23
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Split the anonfd interface into a bare file pointer creation one, and a file pointer creation plus install one. There are cases, like the usage of eventfds inside other kernel interfaces, where the file pointer created by anonfd needs to be used inside the initialization of other structures. As it is right now, as soon as anon_inode_getfd() returns, the kenrle can race with userspace closing the newly installed file descriptor. This patch, while keeping the old anon_inode_getfd(), introduces a new anon_inode_getfile() (whose services are reused in anon_inode_getfd()) that allows to split the file creation phase and the fd install one. Once all the kernel structures are initialized, the code can call the proper fd_install(). Gregory manifested the need for something like this inside KVM. Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: James Morris <jmorris@namei.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Gregory Haskins <ghaskins@novell.com> Acked-by: Serge Hallyn <serue@us.ibm.com> Acked-by: Roland Dreier <rolandd@cisco.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* eventfd: revised interface and cleanupsDavide Libenzi2009-06-30
| | | | | | | | | | | | | | | | | | | | | Change the eventfd interface to de-couple the eventfd memory context, from the file pointer instance. Without such change, there is no clean way to racely free handle the POLLHUP event sent when the last instance of the file* goes away. Also, now the internal eventfd APIs are using the eventfd context instead of the file*. This patch is required by KVM's IRQfd code, which is still under development. Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: Gregory Haskins <ghaskins@novell.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Benjamin LaHaise <bcrl@kvack.org> Cc: Avi Kivity <avi@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* eventfd: improve support for semaphore-like behaviorDavide Libenzi2009-04-01
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | People started using eventfd in a semaphore-like way where before they were using pipes. That is, counter-based resource access. Where a "wait()" returns immediately by decrementing the counter by one, if counter is greater than zero. Otherwise will wait. And where a "post(count)" will add count to the counter releasing the appropriate amount of waiters. If eventfd the "post" (write) part is fine, while the "wait" (read) does not dequeue 1, but the whole counter value. The problem with eventfd is that a read() on the fd returns and wipes the whole counter, making the use of it as semaphore a little bit more cumbersome. You can do a read() followed by a write() of COUNTER-1, but IMO it's pretty easy and cheap to make this work w/out extra steps. This patch introduces a new eventfd flag that tells eventfd to only dequeue 1 from the counter, allowing simple read/write to make it behave like a semaphore. Simple test here: http://www.xmailserver.org/eventfd-sem.c To be back-compatible with earlier kernels, userspace applications should probe for the availability of this feature via #ifdef EFD_SEMAPHORE fd = eventfd2 (CNT, EFD_SEMAPHORE); if (fd == -1 && errno == EINVAL) <fallback> #else <fallback> #endif Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: <linux-api@vger.kernel.org> Tested-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* flag parameters: NONBLOCK in eventfdUlrich Drepper2008-07-24
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch adds support for the EFD_NONBLOCK flag to eventfd2. The additional changes needed are minimal. The following test must be adjusted for architectures other than x86 and x86-64 and in case the syscall numbers changed. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ #include <fcntl.h> #include <stdio.h> #include <unistd.h> #include <sys/syscall.h> #ifndef __NR_eventfd2 # ifdef __x86_64__ # define __NR_eventfd2 290 # elif defined __i386__ # define __NR_eventfd2 328 # else # error "need __NR_eventfd2" # endif #endif #define EFD_NONBLOCK O_NONBLOCK int main (void) { int fd = syscall (__NR_eventfd2, 1, 0); if (fd == -1) { puts ("eventfd2(0) failed"); return 1; } int fl = fcntl (fd, F_GETFL); if (fl == -1) { puts ("fcntl failed"); return 1; } if (fl & O_NONBLOCK) { puts ("eventfd2(0) sets non-blocking mode"); return 1; } close (fd); fd = syscall (__NR_eventfd2, 1, EFD_NONBLOCK); if (fd == -1) { puts ("eventfd2(EFD_NONBLOCK) failed"); return 1; } fl = fcntl (fd, F_GETFL); if (fl == -1) { puts ("fcntl failed"); return 1; } if ((fl & O_NONBLOCK) == 0) { puts ("eventfd2(EFD_NONBLOCK) does not set non-blocking mode"); return 1; } close (fd); puts ("OK"); return 0; } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Signed-off-by: Ulrich Drepper <drepper@redhat.com> Acked-by: Davide Libenzi <davidel@xmailserver.org> Cc: Michael Kerrisk <mtk.manpages@googlemail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* flag parameters: eventfdUlrich Drepper2008-07-24
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch adds the new eventfd2 syscall. It extends the old eventfd syscall by one parameter which is meant to hold a flag value. In this patch the only flag support is EFD_CLOEXEC which causes the close-on-exec flag for the returned file descriptor to be set. A new name EFD_CLOEXEC is introduced which in this implementation must have the same value as O_CLOEXEC. The following test must be adjusted for architectures other than x86 and x86-64 and in case the syscall numbers changed. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ #include <fcntl.h> #include <stdio.h> #include <unistd.h> #include <sys/syscall.h> #ifndef __NR_eventfd2 # ifdef __x86_64__ # define __NR_eventfd2 290 # elif defined __i386__ # define __NR_eventfd2 328 # else # error "need __NR_eventfd2" # endif #endif #define EFD_CLOEXEC O_CLOEXEC int main (void) { int fd = syscall (__NR_eventfd2, 1, 0); if (fd == -1) { puts ("eventfd2(0) failed"); return 1; } int coe = fcntl (fd, F_GETFD); if (coe == -1) { puts ("fcntl failed"); return 1; } if (coe & FD_CLOEXEC) { puts ("eventfd2(0) sets close-on-exec flag"); return 1; } close (fd); fd = syscall (__NR_eventfd2, 1, EFD_CLOEXEC); if (fd == -1) { puts ("eventfd2(EFD_CLOEXEC) failed"); return 1; } coe = fcntl (fd, F_GETFD); if (coe == -1) { puts ("fcntl failed"); return 1; } if ((coe & FD_CLOEXEC) == 0) { puts ("eventfd2(EFD_CLOEXEC) does not set close-on-exec flag"); return 1; } close (fd); puts ("OK"); return 0; } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [akpm@linux-foundation.org: add sys_ni stub] Signed-off-by: Ulrich Drepper <drepper@redhat.com> Acked-by: Davide Libenzi <davidel@xmailserver.org> Cc: Michael Kerrisk <mtk.manpages@googlemail.com> Cc: <linux-arch@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Remove "#ifdef __KERNEL__" checks from unexported headersRobert P. J. Day2008-04-30
| | | | | | | | | | | | Remove the "#ifdef __KERNEL__" tests from unexported header files in linux/include whose entire contents are wrapped in that preprocessor test. Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* eventfd: clean compile when CONFIG_EVENTFD=nRandy Dunlap2007-06-28
| | | | | | | | | | | | Fix gcc warning and add parameter checking when CONFIG_EVENTFD=n: fs/aio.c: In function 'aio_complete': fs/aio.c:955: warning: statement with no effect Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* signal/timer/event: eventfd coreDavide Libenzi2007-05-11
This is a very simple and light file descriptor, that can be used as event wait/dispatch by userspace (both wait and dispatch) and by the kernel (dispatch only). It can be used instead of pipe(2) in all cases where those would simply be used to signal events. Their kernel overhead is much lower than pipes, and they do not consume two fds. When used in the kernel, it can offer an fd-bridge to enable, for example, functionalities like KAIO or syslets/threadlets to signal to an fd the completion of certain operations. But more in general, an eventfd can be used by the kernel to signal readiness, in a POSIX poll/select way, of interfaces that would otherwise be incompatible with it. The API is: int eventfd(unsigned int count); The eventfd API accepts an initial "count" parameter, and returns an eventfd fd. It supports poll(2) (POLLIN, POLLOUT, POLLERR), read(2) and write(2). The POLLIN flag is raised when the internal counter is greater than zero. The POLLOUT flag is raised when at least a value of "1" can be written to the internal counter. The POLLERR flag is raised when an overflow in the counter value is detected. The write(2) operation can never overflow the counter, since it blocks (unless O_NONBLOCK is set, in which case -EAGAIN is returned). But the eventfd_signal() function can do it, since it's supposed to not sleep during its operation. The read(2) function reads the __u64 counter value, and reset the internal value to zero. If the value read is equal to (__u64) -1, an overflow happened on the internal counter (due to 2^64 eventfd_signal() posts that has never been retired - unlickely, but possible). The write(2) call writes an __u64 count value, and adds it to the current counter. The eventfd fd supports O_NONBLOCK also. On the kernel side, we have: struct file *eventfd_fget(int fd); int eventfd_signal(struct file *file, unsigned int n); The eventfd_fget() should be called to get a struct file* from an eventfd fd (this is an fget() + check of f_op being an eventfd fops pointer). The kernel can then call eventfd_signal() every time it wants to post an event to userspace. The eventfd_signal() function can be called from any context. An eventfd() simple test and bench is available here: http://www.xmailserver.org/eventfd-bench.c This is the eventfd-based version of pipetest-4 (pipe(2) based): http://www.xmailserver.org/pipetest-4.c Not that performance matters much in the eventfd case, but eventfd-bench shows almost as double as performance than pipetest-4. [akpm@linux-foundation.org: fix i386 build] [akpm@linux-foundation.org: add sys_eventfd to sys_ni.c] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>