Date: Sun, 22 May 2016 18:22:58 -0700 From: Matthew Macy <mmacy@nextbsd.org> To: "Joerg Sonnenberger" <joerg@bec.de> Cc: "<freebsd-hackers@freebsd.org>" <freebsd-hackers@freebsd.org> Subject: Re: read(2) and thus bsdiff is limited to 2^31 bytes Message-ID: <154db353935.dd5e87c1133922.4370692881788049491@nextbsd.org> In-Reply-To: <20160522231203.GB25503@britannica.bec.de> References: <b2515cae-b75d-66e9-4207-3cf100ab3ab0@erdgeist.org> <20160522225414.GB24398@britannica.bec.de> <154dab43060.11208cdfd132112.2616144627831899155@nextbsd.org> <20160522231203.GB25503@britannica.bec.de>
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---- On Sun, 22 May 2016 16:12:03 -0700 Joerg Sonnenberger <joerg@bec.de> wrote ---- > On Sun, May 22, 2016 at 04:02:02PM -0700, Matthew Macy wrote: > > > > > > > > ---- On Sun, 22 May 2016 15:54:14 -0700 Joerg Sonnenberger <joerg@bec.de> wrote ---- > > > On Sun, May 22, 2016 at 10:54:30PM +0200, Dirk Engling wrote: > > > > When trying to bsdiff two DVD images, I noticed it failing due to > > > > read(2) returning EINVAL to the tool. man 2 read says, this would only > > > > happen for a negative value for fildes, which clearly was not true. > > > > > > I would classify that as implementation bug. It seems perfectly sensible > > > to turn overly large requests into a short read/write, even for blocking > > > files. But erroring out seems to be quite wrong to me. > > > > > > > read(2) takes a size_t so this is clearly an internal bug where it's an int and treating it as a negative value. > > Not exactly. The reason for cutting it off are many fold. Using int in > the kernel is one argument. The requirement for locking the IO range for > concurrent read/write operations from other threads is a bigger > argument. > That still doesn't justify EINVAL as a return. Does read(2) need to make atomicity guarantees? -M
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