Date: Tue, 06 Jan 2009 08:51:18 +0200 From: Danny Braniss <danny@cs.huji.ac.il> To: rick-freebsd2008@kiwi-computer.com Cc: freebsd-stable@FreeBSD.ORG Subject: Re: newfs(8) parameters from "dumpfs -m" have bad -s value? Message-ID: <E1LK5mY-0008AF-R5@kabab.cs.huji.ac.il> In-Reply-To: <20090105221352.GB35524@keira.kiwi-computer.com> References: <20090102153455.GR4100@albert.catwhisker.org> <200901051923.n05JNrwt038325@lurza.secnetix.de> <20090105221352.GB35524@keira.kiwi-computer.com>
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> On Mon, Jan 05, 2009 at 08:23:53PM +0100, Oliver Fromme wrote:
> >
> > This seems to be a bug in dumpfs(8). It simply prints
> > the value of the fs_size field of the superblock, which
> > is wrong.
> >
> > The -s option of newfs(8) expects the available size in
> > sectors (i.e. 512 bytes), but the fs_size field contains
> > the size of the file system in 2KB units. This seems to
> > be the fragment size, but I'm not sure if this is just
>
> This *is* the fragment size. UFS/FFS uses the plain term "block" to mean
> the fragment size. All blocks are indexed with this number, unlike "block
> size" which is almost always 8 fragments ("blocks"). Confusing.
>
> > So, dumpfs(8) needs to be fixed to perform the proper
> > calculations when printing the value for the -s option.
> > Unfortunately I'm not sufficiently much of a UFS guru
> > to offer a fix. My best guess would be to multiply the
> > fs_size value by the fragment size (measured in 512 byte
> > units), i.e. multiply by 4 in the most common case.
> > But I'm afraid the real solution is not that simple.
>
> The sector size and filesystem size parameters in newfs are remnants.
> Everything is converted to number of media sectors (sector size as
> specified by the device). So one could assume for dumpfs to always use
> 512, since it's rarely different, and multiply fs_size by fs_fsize and
> divide by 512, and then output "-S 512".
>
don't assume 512, in the iscsi world I have seen all kinds of sector sizes,
making it a PITA to get things right.
> Better yet would be to add a parameter ("-z" perhaps) to newfs(8) to accept
> number of bytes instead of multiples of sectorsize.
>
> I would be willing to write up patches for dumpfs and newfs to both add the
> raw byte size and the 512-byte sector size handling to correct said
> mistake, unless someone else would rather.
>
> -- Rick C. Petty
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