diff options
author | J. Bruce Fields <bfields@citi.umich.edu> | 2008-02-07 00:13:35 -0800 |
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committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-07 08:42:17 -0800 |
commit | e9b1a4d160f68397d29183ce76af1cc774508aba (patch) | |
tree | 029375c6bb3f0268dcd3aca373066acaec2e59ca /Documentation/dnotify.txt | |
parent | 4a6b88ca3d9a301b496d6bfc18bc40c78fbb3669 (diff) |
Documentation: move dnotify.txt to filesystems/
I'm inclined to think dnotify belongs in filesystems/.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/dnotify.txt')
-rw-r--r-- | Documentation/dnotify.txt | 99 |
1 files changed, 0 insertions, 99 deletions
diff --git a/Documentation/dnotify.txt b/Documentation/dnotify.txt deleted file mode 100644 index 6984fca6002a..000000000000 --- a/Documentation/dnotify.txt +++ /dev/null @@ -1,99 +0,0 @@ - Linux Directory Notification - ============================ - - Stephen Rothwell <sfr@canb.auug.org.au> - -The intention of directory notification is to allow user applications -to be notified when a directory, or any of the files in it, are changed. -The basic mechanism involves the application registering for notification -on a directory using a fcntl(2) call and the notifications themselves -being delivered using signals. - -The application decides which "events" it wants to be notified about. -The currently defined events are: - - DN_ACCESS A file in the directory was accessed (read) - DN_MODIFY A file in the directory was modified (write,truncate) - DN_CREATE A file was created in the directory - DN_DELETE A file was unlinked from directory - DN_RENAME A file in the directory was renamed - DN_ATTRIB A file in the directory had its attributes - changed (chmod,chown) - -Usually, the application must reregister after each notification, but -if DN_MULTISHOT is or'ed with the event mask, then the registration will -remain until explicitly removed (by registering for no events). - -By default, SIGIO will be delivered to the process and no other useful -information. However, if the F_SETSIG fcntl(2) call is used to let the -kernel know which signal to deliver, a siginfo structure will be passed to -the signal handler and the si_fd member of that structure will contain the -file descriptor associated with the directory in which the event occurred. - -Preferably the application will choose one of the real time signals -(SIGRTMIN + <n>) so that the notifications may be queued. This is -especially important if DN_MULTISHOT is specified. Note that SIGRTMIN -is often blocked, so it is better to use (at least) SIGRTMIN + 1. - -Implementation expectations (features and bugs :-)) ---------------------------- - -The notification should work for any local access to files even if the -actual file system is on a remote server. This implies that remote -access to files served by local user mode servers should be notified. -Also, remote accesses to files served by a local kernel NFS server should -be notified. - -In order to make the impact on the file system code as small as possible, -the problem of hard links to files has been ignored. So if a file (x) -exists in two directories (a and b) then a change to the file using the -name "a/x" should be notified to a program expecting notifications on -directory "a", but will not be notified to one expecting notifications on -directory "b". - -Also, files that are unlinked, will still cause notifications in the -last directory that they were linked to. - -Configuration -------------- - -Dnotify is controlled via the CONFIG_DNOTIFY configuration option. When -disabled, fcntl(fd, F_NOTIFY, ...) will return -EINVAL. - -Example -------- - - #define _GNU_SOURCE /* needed to get the defines */ - #include <fcntl.h> /* in glibc 2.2 this has the needed - values defined */ - #include <signal.h> - #include <stdio.h> - #include <unistd.h> - - static volatile int event_fd; - - static void handler(int sig, siginfo_t *si, void *data) - { - event_fd = si->si_fd; - } - - int main(void) - { - struct sigaction act; - int fd; - - act.sa_sigaction = handler; - sigemptyset(&act.sa_mask); - act.sa_flags = SA_SIGINFO; - sigaction(SIGRTMIN + 1, &act, NULL); - - fd = open(".", O_RDONLY); - fcntl(fd, F_SETSIG, SIGRTMIN + 1); - fcntl(fd, F_NOTIFY, DN_MODIFY|DN_CREATE|DN_MULTISHOT); - /* we will now be notified if any of the files - in "." is modified or new files are created */ - while (1) { - pause(); - printf("Got event on fd=%d\n", event_fd); - } - } |