Re: [fuse-devel] When to flush cache

[Goswin v. B. <gos...@we...>]

Miklos Szeredi <mi...@sz...> writes:

> On Thu, 07 Aug 2008, Goswin von Brederlow wrote:
>> > Linux's default is to flush data from the cache that is older than 30
>> > seconds, and do such a run every 5 seconds.  It also has limits for
>> > the size of the data that can be buffered this way.
>> >
>> > Miklos
>> 
>> Does fuse have any hook for such a 5-second-tick?
>
> No.
>
>> Actually I can think of 2 tick() modes:
>> 
>> 1) call every 5 seconds no matter what (unless old tick is still
>>    running)
>> 2) call after 5 seconds without request
>> 
>> Obviously the second can be more or less implemented with the first
>> but it might be worth having a flag when registering such a tick()
>> callback.
>> 
>> 
>> Alternatively how would you imlement this, esspecially for a single
>> threaded FS? I don't want the tick() to run in parallel with other
>> operations.
>
> You'd have to implement your own event loop in that case.  Not that
> difficult: basically just poll() followed by fuse_chan_recv() and
> fuse_session_process().
>
> Miklos

I tried this with select instead of poll:

--- fuse-2.7.3.orig/lib/fuse_kern_chan.c
+++ fuse-2.7.3/lib/fuse_kern_chan.c
@@ -14,6 +14,7 @@
 #include <errno.h>
 #include <unistd.h>
 #include <assert.h>
+#include <sys/select.h>
 
 static int fuse_kern_chan_receive(struct fuse_chan **chp, char *buf,
                                  size_t size)
@@ -22,9 +23,21 @@
        int err;
        ssize_t res;
        struct fuse_session *se = fuse_chan_session(ch);
+       fd_set rfds;
+       struct timeval timeout;
        assert(se != NULL);
-
+       FD_ZERO(&rfds);
+       FD_SET(fuse_chan_fd(ch), &rfds);
 restart:
+       timeout.tv_sec = 1;
+       timeout.tv_usec = 0;
+       res = select(fuse_chan_fd(ch), &rfds, NULL, NULL, &timeout);
+       if (res == -1) {
+               perror("fuse: select");
+       } else if (res == 0) {
+               printf("fuse: --tick--\n");
+               goto restart;
+       }
        res = read(fuse_chan_fd(ch), buf, size);
        err = errno;
 

Problem there is that select will always wait 1 second and always
returns 0 and goes into an endless loop. The fuse FD does not seem to
support select().

Any chance poll would work?

MfG
        Goswin