Date: Sat, 14 Jul 2007 21:18:45 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Bruce Evans <brde@optusnet.com.au> Cc: freebsd-fs@freebsd.org, Brian Chu <chub@freebsd.org> Subject: Re: msdosfs header unification patch Message-ID: <20070714211354.I1555@besplex.bde.org> In-Reply-To: <20070713223111.P2242@besplex.bde.org> References: <47a4f3080707130119xbee4477y3e96d27763f793aa@mail.gmail.com> <20070713223111.P2242@besplex.bde.org>
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On Fri, 13 Jul 2007, Bruce Evans wrote: > On Fri, 13 Jul 2007, Brian Chu wrote: > % ... > % - /* Check backup FSInfo? XXX > */ > % + > % + /* Unnecessary to check the backup FSInfo because there isn't > % + * an physical backup copy of the FSInfo block. There's only a > % + * backup of the FSInfo block number, which was checked (bsBPB) above. > % + */ > % } > > But there is a physical backup FSinfo. > > The normal layout is: > > main boot sector (sector 0) > fsinfo (sector 1, but can be anywhere) > second boot sector (next sector? -- no pointer to this) > fsisig4 checks/clobbers here > backup main boot sector (sector 3, but can be anywhere) Actually, it is sector 6. Sectors 3-5 are unused. Microsoft docs say not to use any other layout (for portability, since some utilities hard-code 6) ... > backup fsinfo (next sector? -- no pointer to this, since backup > main boot sector can't have a different pointer than main bs) > backup second boot sector (next sector?) > backup fsisig4 would check/clobber here > > newfs_msdos omits the second boot sector and creates the following layout: > > main boot sector (sector 0) > fsinfo (sector 1) > backup main boot sector (sector 2) > fsisig4 checks/clobbers here > backup fsinfo (sector 3) > backup fsisig4 would check/clobber outside of all boot sectors ... so this is a very unusual layout and shouldn't be produced by default. Bruce
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