https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225586
Bug ID: 225586
Summary: ftruncate+mmap+fsync fails for small maps
Product: Base System
Version: 11.1-STABLE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: misc
Assignee: freebsd-bugs@FreeBSD.org
Reporter: tris_v...@hotmail.com
Created attachment 190220
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=190220&action=edit
test on tmp filesystem that can be unmounted
When doing an ftruncate+mmap+fsync to a size less than 512 bytes the data never
seems to be sync'd properly to disk.
This work fine on the latest 11.1-RELEASE but not the latest 11.1-STABLE. It is
also ok if the ftruncate is to the existing file size.
While the mapped changes are visible in the file before an umount, after even a
failed umount, the changes are no longer present.
(non-error checked) C code below.
After running the binary, check the contents of the file (eg hd) and it will be
all 0xFF. Then, umount the filesystem you are on*. Then check the contents of
the file again. It will now be 0x01.
Running extra sync's or fsync's from the command line before the umount doesn't
seem to help.
* The umount should fail but still shows the problem. However note it doesn't
seem to work with the error given for the root filesystem "/".
I've also attached a script that creates a filesystem to umount
---
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <sys/mman.h>
int
main (int argc, char *argv[])
{
int fd;
size_t i, size1, size2;
char *data;
char *filename;
char pattern = 0x01;
if (argc < 2) {
fprintf(stderr, "Usage: %s filename size1 size2\n", argv[0]);
exit(1);
}
filename = argv[1];
size1 = atoi(argv[2]);
size2 = atoi(argv[3]);
fd = open(filename, O_RDWR | O_TRUNC | O_CREAT, 0644);
for (i = 0; i < size1; i++)
write(fd, &pattern, 1);
close(fd);
fd = open(filename, O_RDWR, 0644);
ftruncate(fd, size2);
data = mmap(NULL, size2, PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
memset(data, 0xFF, size2);
fsync(fd);
munmap(data, size2);
close(fd);
}
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