Timestamp of file modified through mmap are not changed in 2.6
From: Xavier Roche (roche+kml2_at_exalead.com)
Date: 04/08/05
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Date: Fri, 08 Apr 2005 17:17:00 +0200 To: linux-kernel@vger.kernel.org
Timestamp of file modified through mmap are not changed in 2.6 (even
after msync()). Observations on 2.4 and 2.6 kernels:
- on 2.4, timestamps are altered a few seconds after the program exits.
- on 2.6, timestamps are never altered.
Is this behaviour a normal behaviour ?
Program example to reproduce the bug (you need to create a "test" file
in the current directory first):
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
int main(void) {
int fd = open("test", O_RDWR);
struct stat st;
char* file;
if (fd == -1) {
printf("error opening file\n");
return 1;
}
if (fstat(fd, &st) != 0) {
printf("error fstating file\n");
return 1;
}
if (st.st_size == 0) {
printf("error empty file\n");
return 1;
}
printf("Modified date before change: %u\n", st.st_mtime);
file = mmap(NULL, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (file == NULL) {
printf("error mmaping file");
return 1;
}
file[0] = file[0] + 1;
if (msync((void*) file, st.st_size, MS_SYNC) != 0) {
printf("error syncing file");
return 1;
}
if (munmap(file, st.st_size) != 0) {
printf("error closing file");
return 1;
}
if (fstat(fd, &st) != 0) {
printf("error fstating file\n");
return 1;
}
printf("Modified date after change: %u\n", st.st_mtime);
return 0;
}
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