Date: Wed, 29 Sep 2004 19:49:16 -0700 From: Nehal <nehalmistry@gmx.net> To: David Schultz <das@FreeBSD.ORG> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: data blocks question Message-ID: <20040929194916.00000f43@nehal> In-Reply-To: <20040929230929.GA31474@VARK.MIT.EDU> References: <20040929101403.000027aa@nehal> <20040929204233.GB30629@VARK.MIT.EDU> <20040929154328.00001444@nehal> <20040929230929.GA31474@VARK.MIT.EDU>
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On Wed, 29 Sep 2004 19:09:29 -0400 David Schultz <das@FreeBSD.ORG> wrote: > On Wed, Sep 29, 2004, Nehal wrote: > > On Wed, 29 Sep 2004 16:42:33 -0400 > > David Schultz <das@FreeBSD.ORG> wrote: > > > > > On Wed, Sep 29, 2004, Nehal wrote: > > > > on my ufs2 partition, there is a file that has a size of > > > > 65536, and has 2 direct blocks only. the block size of the > > > > fs is 16k and fragment block size is 2k. > > > > > > > > how can this be possible? wouldn't 2 direct blocks mean > > > > that the maximum size is 2x16k = 32k? or am i not > > > > understanding something correctly? > > > > > > > > i've made a copy of the file, and the new file has 4 > > > > direct blocks. > > > > > > > > it is a binary file, and i can read it fine (ie, cat it). > > > > i've done fsck on the filesystem and it found no problem. > > > > > > Yes, UFS supports sparse files. That is, you can have a > > > file with parts you haven't written to, and the blocks for > > > those parts won't be allocated. The cp utility doesn't know > > > about this, though, so copies will have the ``holes'' filled > > > with zeroes. > > > > > > > how would i determine the offset and length of these 'holes' > > for sparse files? > > It's an implementation detail, so you're not supposed to need to > know most of the time. You can use fsdb to find out. > i would like to know how it is implemented. is there somewhere in the freebsd source that i can find this info? Nehal
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