Date: Sat, 16 Jun 2012 21:04:26 +0100 From: Chris Rees <utisoft@gmail.com> To: Xin LI <delphij@gmail.com> Cc: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>, freebsd-hackers@freebsd.org Subject: Re: BIO_DELETE equivalent for file on FFS filesystem Message-ID: <CADLo83-dZD5C2Fk3ZTH9z=pXHn8BtYzZQqUBG6HCkHZKe1=P8Q@mail.gmail.com> In-Reply-To: <CAGMYy3sWPMCnttUtJhJCFTtPtgfWWUO1tgK%2BRYOE3QQpg=%2Bw1A@mail.gmail.com> References: <alpine.BSF.2.00.1205261704590.70782@wojtek.tensor.gdynia.pl> <4FD94240.6060806@delphij.net> <alpine.BSF.2.00.1206140647080.72545@wojtek.tensor.gdynia.pl> <CADLo83-T%2B4W2aUKc=-CEUrOqwCq5aqipt-fK=BBboQVNJ3qcWQ@mail.gmail.com> <CAGMYy3sWPMCnttUtJhJCFTtPtgfWWUO1tgK%2BRYOE3QQpg=%2Bw1A@mail.gmail.com>
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On Jun 16, 2012 8:37 PM, "Xin LI" <delphij@gmail.com> wrote: > > On Sat, Jun 16, 2012 at 12:01 PM, Chris Rees <utisoft@gmail.com> wrote: > > On Jun 14, 2012 5:49 AM, "Wojciech Puchar" < wojtek@wojtek.tensor.gdynia.pl> > > wrote: > >>>> > >>>> file to take 900MB or... can i call some system function to "punch" > >>>> holes? > >>> > >>> > >>> I think you can only truncate the file at this time, pretty much like > >>> brk() works for memory. > >> > >> > >> > >> BAD. suppose i keep windoze VM image on filesystem which takes 10GB but > > uses 5GB. > >> > >> i could write simple program to find out what blocks are unused and > > then...do nothing. > >> > > > > What if you cp it? > > That would be a dd(1) unless we teach cp(1) how to do sparse. I think > what he wanted is to tell the OS "I don't need block XX - YY anymore" > and the OS creates a sparse hole, which is not available at this time. Sorry, I must have misread. I take it cp would take a file with holes and only copy the data part? i.e. take a 10G file of which 5G is a hole, you'd end up with a 5G file? Chris
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