On 4/30/12 12:19 PM, Daniel Drake wrote: > Hi, > > OLPC has started using ext4 online resizing to grow our filesystems to > use the whole SD card on first boot - something we never did before. > Working very nicely, thanks! > > I'm trying to simplify/improve the scripts involved in doing this. > > How can I programatically check if an ext4 fs already fills its > partition, or if it has room to grow? > > > The numbers produced by dumpe2fs (e.g. block count) or "df" don't seem > to exactly line up with the sizes produced by fdisk. Do you have an example of this? For starters, use fdisk -u to get 512-byte sector units, otherwise it's just inscrutable CHS magic. i.e.: # fdisk -lu /dev/sda2 Disk /dev/sda2: 526 MB, 526417920 bytes 255 heads, 63 sectors/track, 64 cylinders, total 1028160 sectors Units = sectors of 1 * 512 = 512 bytes so 1028160 512-byte sectors. # dumpe2fs -h /dev/sda2 | grep "Block count\|Block size" dumpe2fs 1.42.2 (27-Mar-2012) Block count: 514080 Block size: 1024 so 514080 1k blocks, or 1028160 512-byte sectors, so bingo, it's full. Of course you can't use an odd sector hanging off the end, so you'd need to do a little rounding down to the nearest fs block size. Otherwise, it should be straightforward. Or, FWIW, it's harmless to invoke resize2fs if the fs already fills the partition; it should just exit with a no-op. > One easy solution, if possible, would be to find out the number of the > last sector used by the filesystem. I could then very easily compare > this to the "end" information found in sysfs for the partition. Then I > can make the decision on whether to grow or not. dumpe2fs should certainly be able to tell you. Mounting the fs, and doing statfs would, as well (f_blocks). There should also be libext2fs functions you could use if you want to do it in C... -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
