view Documentation/dnotify.txt @ 452:c7ed6fe5dca0

kexec: dont initialise regions in reserve_memory()

There is no need to initialise efi_memmap_res and boot_param_res in
reserve_memory() for the initial xen domain as it is done in
machine_kexec_setup_resources() using values from the kexec hypercall.

Signed-off-by: Simon Horman <horms@verge.net.au>
author Keir Fraser <keir.fraser@citrix.com>
date Thu Feb 28 10:55:18 2008 +0000 (2008-02-28)
parents 831230e53067
line source
1 Linux Directory Notification
2 ============================
4 Stephen Rothwell <sfr@canb.auug.org.au>
6 The intention of directory notification is to allow user applications
7 to be notified when a directory, or any of the files in it, are changed.
8 The basic mechanism involves the application registering for notification
9 on a directory using a fcntl(2) call and the notifications themselves
10 being delivered using signals.
12 The application decides which "events" it wants to be notified about.
13 The currently defined events are:
15 DN_ACCESS A file in the directory was accessed (read)
16 DN_MODIFY A file in the directory was modified (write,truncate)
17 DN_CREATE A file was created in the directory
18 DN_DELETE A file was unlinked from directory
19 DN_RENAME A file in the directory was renamed
20 DN_ATTRIB A file in the directory had its attributes
21 changed (chmod,chown)
23 Usually, the application must reregister after each notification, but
24 if DN_MULTISHOT is or'ed with the event mask, then the registration will
25 remain until explicitly removed (by registering for no events).
27 By default, SIGIO will be delivered to the process and no other useful
28 information. However, if the F_SETSIG fcntl(2) call is used to let the
29 kernel know which signal to deliver, a siginfo structure will be passed to
30 the signal handler and the si_fd member of that structure will contain the
31 file descriptor associated with the directory in which the event occurred.
33 Preferably the application will choose one of the real time signals
34 (SIGRTMIN + <n>) so that the notifications may be queued. This is
35 especially important if DN_MULTISHOT is specified. Note that SIGRTMIN
36 is often blocked, so it is better to use (at least) SIGRTMIN + 1.
38 Implementation expectations (features and bugs :-))
39 ---------------------------
41 The notification should work for any local access to files even if the
42 actual file system is on a remote server. This implies that remote
43 access to files served by local user mode servers should be notified.
44 Also, remote accesses to files served by a local kernel NFS server should
45 be notified.
47 In order to make the impact on the file system code as small as possible,
48 the problem of hard links to files has been ignored. So if a file (x)
49 exists in two directories (a and b) then a change to the file using the
50 name "a/x" should be notified to a program expecting notifications on
51 directory "a", but will not be notified to one expecting notifications on
52 directory "b".
54 Also, files that are unlinked, will still cause notifications in the
55 last directory that they were linked to.
57 Configuration
58 -------------
60 Dnotify is controlled via the CONFIG_DNOTIFY configuration option. When
61 disabled, fcntl(fd, F_NOTIFY, ...) will return -EINVAL.
63 Example
64 -------
66 #define _GNU_SOURCE /* needed to get the defines */
67 #include <fcntl.h> /* in glibc 2.2 this has the needed
68 values defined */
69 #include <signal.h>
70 #include <stdio.h>
71 #include <unistd.h>
73 static volatile int event_fd;
75 static void handler(int sig, siginfo_t *si, void *data)
76 {
77 event_fd = si->si_fd;
78 }
80 int main(void)
81 {
82 struct sigaction act;
83 int fd;
85 act.sa_sigaction = handler;
86 sigemptyset(&act.sa_mask);
87 act.sa_flags = SA_SIGINFO;
88 sigaction(SIGRTMIN + 1, &act, NULL);
90 fd = open(".", O_RDONLY);
91 fcntl(fd, F_SETSIG, SIGRTMIN + 1);
93 /* we will now be notified if any of the files
94 in "." is modified or new files are created */
95 while (1) {
96 pause();
97 printf("Got event on fd=%d\n", event_fd);
98 }
99 }