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Subject[sample] mem_notify v6: usage example
this is usage example of /dev/mem_notify.

Daniel Spang create original version.
kosaki add fasync related code.


Signed-off-by: Daniel Spang <daniel.spang@gmail.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

---
Documentation/mem_notify.c | 120 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 120 insertions(+)
Index: b/Documentation/mem_notify.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ b/Documentation/mem_notify.c 2008-02-10 00:44:00.000000000 +0900
@@ -0,0 +1,120 @@
+/*
+ * Allocate 10 MB each second. Exit on notification.
+ */
+
+#define _GNU_SOURCE
+
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <poll.h>
+#include <pthread.h>
+#include <errno.h>
+#include <signal.h>
+
+int count = 0;
+int size = 10;
+
+void *do_alloc()
+{
+ for(;;) {
+ int *buffer;
+ buffer = mmap(NULL, size*1024*1024,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (buffer == MAP_FAILED) {
+ perror("mmap");
+ exit(EXIT_FAILURE);
+ }
+ memset(buffer, 1 , size*1024*1024);
+
+ printf("-");
+ fflush(stdout);
+
+ count++;
+ sleep(1);
+ }
+}
+
+int wait_for_notification(struct pollfd *pfd)
+{
+ int ret;
+ read(pfd->fd, 0, 0);
+ ret = poll(pfd, 1, -1); /* wake up when low memory */
+ if (ret == -1 && errno != EINTR) {
+ perror("poll");
+ exit(EXIT_FAILURE);
+ }
+ return ret;
+}
+
+void do_free()
+{
+ int fd;
+ struct pollfd pfd;
+
+ fd = open("/dev/mem_notify", O_RDONLY);
+ if (fd == -1) {
+ perror("open");
+ exit(EXIT_FAILURE);
+ }
+
+ pfd.fd = fd;
+ pfd.events = POLLIN;
+ for(;;)
+ if (wait_for_notification(&pfd) > 0) {
+ printf("\nGot notification, allocated %d MB\n",
+ size * count);
+ exit(EXIT_SUCCESS);
+ }
+}
+
+void do_free_signal()
+{
+ int fd;
+ int flags;
+
+ fd = open("/dev/mem_notify", O_RDONLY);
+ if (fd == -1) {
+ perror("open");
+ exit(EXIT_FAILURE);
+ }
+
+ fcntl(fd, F_SETOWN, getpid());
+ fcntl(fd, F_SETSIG, SIGUSR1);
+
+ flags = fcntl(fd, F_GETFL);
+ fcntl(fd, F_SETFL, flags|FASYNC); /* when low memory, receive SIGUSR1 */
+
+ for(;;)
+ sleep(1);
+}
+
+
+void daniel_exit(int signo)
+{
+ printf("\nGot notification %d, allocated %d MB\n",
+ signo, size * count);
+ exit(EXIT_SUCCESS);
+
+}
+
+int main(int argc, char *argv[])
+{
+ pthread_t allocator;
+
+ if(argc == 2 && (strcmp(argv[1], "-sig") == 0)) {
+ printf("run signal mode\n");
+ signal(SIGUSR1, daniel_exit);
+ pthread_create(&allocator, NULL, do_alloc, NULL);
+ do_free_signal();
+ } else {
+ printf("run poll mode\n");
+ pthread_create(&allocator, NULL, do_alloc, NULL);
+ do_free();
+ }
+ return 0;
+}

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