[dm-devel] lvm not updating reported device size until fs is unmounted (linux kernel 2.6.0-test3)

[Tupshin Harper]

Sorry for the cross-post...wasn't sure where to put this one. Feel free 
to respond on whichever group is more appropriate...

I am experiencing a problem where xfs_growfs would fail to do anything 
unless the fs has been unmounted and remounted before the growfs 
command. This problem (with help from the xfs guys) has been tracked 
down to the device mapper not updating it's reported size until the 
umount takes place.

The code below tests this (aside: it would be nice to have this reported 
in proc), and this example illustrates the problem(lvm_size is what I 
compiled the below code as):
# ./lvm_size /dev/lvm_group_2/debmir
size = 11811160064 bytes, sector size = 512 bytes

# lvextend -L +100M /dev/lvm_group_2/debmir
 Extending logical volume debmir to 11.10 GB
 Logical volume debmir successfully resized

# ./lvm_size /dev/lvm_group_2/debmir
size = 11811160064 bytes, sector size = 512 bytes

# umount /data/debmir
# ./lvm_size /dev/lvm_group_2/debmir
size = 11916017664 bytes, sector size = 512 bytes

-Thanks
-Tupshin

#include <stdio.h>
#include <fcntl.h>
#include <sys/ioctl.h>

#define BLKGETSIZE64   _IOR(0x12,114,sizeof(unsigned long long))
#define BLKSSZGET      _IO(0x12,104)

int main(int argc, char **argv)
{
	unsigned long long size;
	int ssize, fd, error;

	if (argc < 2) {
		fprintf(stderr, "insufficent arguments\n");
		exit(1);
	}
	if ((fd = open(argv[1], O_RDONLY)) < 0) {
		perror(argv[1]);
		exit(1);
	}
	if (ioctl(fd, BLKGETSIZE64, &size) < 0) {
		perror("BLKGETSIZE64");
		exit(1);
	}
	if (ioctl(fd, BLKSSZGET, &ssize) < 0) {
		perror("BLKSSZGET");
		exit(1);
	}
	close(fd);

	printf("size = %lld bytes, sector size = %d bytes\n", size, ssize);
}