On Sat, Dec 22, 2001 at 09:57:23AM -0000, Pichai Raghavan wrote:
> When we look at the ramdisk implementation(rd.c) we see
> that all ramdisk buffers are made immune against buffer
> cache flushing; this means that they will be alive as
> long as kernel is alive. Even on doing a close of
> ramdisk device these buffers are not destroyed. Only place they are destroyed are when ramdisk is made a
> module and module is removed; but since we do not want
> ramdisk as module this does not work for us.
>
> Why does close of ramdisk not invalidate all the
> buffers?
Suppose you want to build a mini root filesystem for an embedded linux
system:
mke2fs /dev/ram0
mount -t ext2 /dev/ram0 /mnt
[populate /mnt as a mini root filesystem with busybox, tinylogin, etc]
umount /dev/ram0
dd if=/dev/ram0 of=rootfs bs=1k
gzip -9 rootfs
Now guess what happens when the ramdisk was destroyed after the
umount...
> WHy is the special treatment given only when
> ramdisk is made as a module?
Because it is good (no, *necessary*) practice that a module frees all
memory it allocated.
If you want to free the memory of a ramdisk, there is an ioctl() for
that:
int fd;
if((fd = open("/dev/ram", O_RDWR)) < 0) {
perror("open");
exit(-1);
}
ioctl(fd, BLKFLSBUF);
close(fd);
Erik
--
J.A.K. (Erik) Mouw, Information and Communication Theory Group, Faculty
of Information Technology and Systems, Delft University of Technology,
PO BOX 5031, 2600 GA Delft, The Netherlands Phone: +31-15-2783635
Fax: +31-15-2781843 Email: J.A.K.Mouw@its.tudelft.nl
WWW: http://www-ict.its.tudelft.nl/~erik/
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