* Regression: File truncate inotify behavior change
@ 2024-02-16 19:53 Paul Lawrence
0 siblings, 0 replies; only message in thread
From: Paul Lawrence @ 2024-02-16 19:53 UTC (permalink / raw
To: Linux kernel; +Cc: Amir Goldstein, Miklos Szeredi, linux-fsdevel
The change:
fsnotify: move fsnotify_open() hook into do_dentry_open()
has modified notification behavior on creat. Specifically, calling
creat on an existing file used to emit a modify then an open
notification, presumably from the file being truncated first. After
this change, there is no modify. I wrote the following test program:
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/inotify.h>
const char *dirname = "test";
const char *filename = "test/file";
int main() {
char buffer[4096];
int size;
char *ptr = buffer;
mkdir(dirname, 0777);
int nfd = inotify_init();
inotify_add_watch(nfd, dirname, IN_ALL_EVENTS);
int fd = creat(filename, 0600);
write(fd, "hello", 5);
close(fd);
size = read(nfd, buffer, sizeof(buffer));
while(size > 0) {
struct inotify_event *ie = (struct inotify_event *) ptr;
printf("%d %u %u %u %s\n", ie->wd, (unsigned) ie->mask, (unsigned)
ie->cookie, (unsigned) ie->len, ie->name);
ptr += sizeof(*ie) + ie->len;
size -= sizeof(*ie) + ie->len;
}
return 0;
}
which demonstrates the change - if you run it twice without this patch, you get:
debian@debian:~$ ./test
1 256 0 16 file
1 32 0 16 file
1 2 0 16 file
1 8 0 16 file
debian@debian:~$ ./test
1 2 0 16 file
1 32 0 16 file
1 2 0 16 file
1 8 0 16 file
but with this patch you get:
debian@debian:~$ ./test
1 256 0 16 file
1 32 0 16 file
1 2 0 16 file
1 8 0 16 file
debian@debian:~$ ./test
1 32 0 16 file
1 2 0 16 file
1 8 0 16 file
(Android has a CTS test that detected this change in behavior. I am
not aware of any actual breakages caused by it, but it seemed worth
surfacing this change so we can decide the best course of action.)
Paul
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2024-02-16 19:53 UTC | newest]
Thread overview: (only message) (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2024-02-16 19:53 Regression: File truncate inotify behavior change Paul Lawrence
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).