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SubjectRe: [PATCH 2/2] updating ctime and mtime at syncing
2008/1/14, Miklos Szeredi <miklos@szeredi.hu>:
> > > http://bugzilla.kernel.org/show_bug.cgi?id=2645
> > >
> > > Changes for updating the ctime and mtime fields for memory-mapped files:
> > >
> > > 1) new flag triggering update of the inode data;
> > > 2) new function to update ctime and mtime for block device files;
> > > 3) new helper function to update ctime and mtime when needed;
> > > 4) updating time stamps for mapped files in sys_msync() and do_fsync();
> > > 5) implementing the feature of auto-updating ctime and mtime.
> >
> > How exactly is this done?
> >
> > Is this catering for this case:
> >
> > 1 page is dirtied through mapping
> > 2 app calls msync(MS_ASYNC)
> > 3 page is written again through mapping
> > 4 app calls msync(MS_ASYNC)
> > 5 ...
> > 6 page is written back
> >
> > What happens at 4? Do we care about this one at all?
>
> Oh, and here's a test program I wrote, that can be used to check this
> behavior. It has two options:
>
> -s use MS_SYNC instead of MS_ASYNC
> -f fork and do the msync on a different mapping
>
> Back then I haven't found a single OS, that fully conformed to all the
> stupid POSIX rules regarding mmaps and ctime/mtime.

Thank you very much for sharing your code.

I'll integrate the MS_ASYNC and fork() test cases into my own unit test.

>
> Miklos
> ----
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <string.h>
> #include <fcntl.h>
> #include <sys/mman.h>
> #include <sys/stat.h>
> #include <sys/wait.h>
>
> static const char *filename;
> static int msync_flag = MS_ASYNC;
> static int msync_fork = 0;
>
> static void print_times(const char *msg)
> {
> struct stat stbuf;
> stat(filename, &stbuf);
> printf("%s\t%li\t%li\t%li\n", msg, stbuf.st_ctime, stbuf.st_mtime,
> stbuf.st_atime);
> }
>
> static void do_msync(void *addr, int len)
> {
> int res;
> if (!msync_fork) {
> res = msync(addr, len, msync_flag);
> if (res == -1) {
> perror("msync");
> exit(1);
> }
> } else {
> int pid = fork();
> if (pid == -1) {
> perror("fork");
> exit(1);
> }
> if (!pid) {
> int fd = open(filename, O_RDWR);
> if (fd == -1) {
> perror("open");
> exit(1);
> }
> addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> if (addr == MAP_FAILED) {
> perror("mmap");
> exit(1);
> }
> res = msync(addr, len, msync_flag);
> if (res == -1) {
> perror("msync");
> exit(1);
> }
> exit(0);
> }
> wait(NULL);
> }
> }
>
> static void usage(const char *progname)
> {
> fprintf(stderr, "usage: %s filename [-sf]\n", progname);
> exit(1);
> }
>
> int main(int argc, char *argv[])
> {
> int res;
> char *addr;
> int fd;
>
> if (argc < 2)
> usage(argv[0]);
>
> filename = argv[1];
> if (argc > 2) {
> if (argc > 3)
> usage(argv[0]);
> if (strcmp(argv[2], "-s") == 0)
> msync_flag = MS_SYNC;
> else if (strcmp(argv[2], "-f") == 0)
> msync_fork = 1;
> else if (strcmp(argv[2], "-sf") == 0 || strcmp(argv[2], "-fs") == 0) {
> msync_flag = MS_SYNC;
> msync_fork = 1;
> } else
> usage(argv[0]);
> }
>
> fd = open(filename, O_RDWR | O_TRUNC | O_CREAT, 0666);
> if (fd == -1) {
> perror(filename);
> return 1;
> }
> print_times("begin");
> sleep(1);
> write(fd, "aaaa\n", 4);
> print_times("write");
> sleep(1);
> addr = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> if (addr == MAP_FAILED) {
> perror("mmap");
> return 1;
> }
> print_times("mmap");
> sleep(1);
>
> addr[1] = 'b';
> print_times("b");
> sleep(1);
> do_msync(addr, 4);
> print_times("msync b");
> sleep(1);
>
> addr[2] = 'c';
> print_times("c");
> sleep(1);
> do_msync(addr, 4);
> print_times("msync c");
> sleep(1);
>
> addr[3] = 'd';
> print_times("d");
> sleep(1);
> res = munmap(addr, 4);
> if (res == -1) {
> perror("munmap");
> return 1;
> }
> print_times("munmap");
> sleep(1);
>
> res = close(fd);
> if (res == -1) {
> perror("close");
> return 1;
> }
> print_times("close");
> sleep(1);
> sync();
> print_times("sync");
>
> return 0;
> }
>
>
>


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