DragonFly kernel List (threaded) for 2008-08
Re: Hammer bootloader
:Is there any reason not to avoid writing in the first 8K? Ext2 on
:Linux for example leaves the first 4K free, and I intend to do the
:same, just to leave space for a boot block in case somebody needs it.
I think there are good arguments to leave significant space at the
beginning, and also good arguments not to. The real issue here is
not so much the filesystem, but the disklabel or partitioner the
filesystem is sitting in.
32 bit disklabels specify block numbers in-band and allow filesystems
to start at block 0, which overlaps the label and boot area. It is for
this reason that filesystems have traditionally reserved some space
at the beginning. One can still use a filesystem that does not reserve
space with a 32 bit disklabel, one simply must start the filesystem at
a higher block number (block 16 is typical, which reserves 8K at the
beginning of the label).
GPT and 64 bit disklabels specify block numbers out-of-band and do not
allow filesystems to start at the real block 0.