Date: Wed, 19 Jan 2011 08:57:29 +0200 From: Daniel Braniss <danny@cs.huji.ac.il> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: freebsd-hackers@freebsd.org, Rick Macklem <rmacklem@uoguelph.ca> Subject: Re: NFS: file too large Message-ID: <E1PfRyz-0000mX-Oa@kabab.cs.huji.ac.il> In-Reply-To: <201101190424.p0J4OkgW006798@apollo.backplane.com> References: <334773590.270506.1295050163687.JavaMail.root@erie.cs.uoguelph.ca> <201101190424.p0J4OkgW006798@apollo.backplane.com>
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> :Well, since a server specifies the maximum file size it can > :handle, it seems good form to check for that in the client. > :(Although I'd agree that a server shouldn't crash if a read/write > : that goes beyond that limit.) > : > :Also, as Matt notes, off_t is signed. As such, it looks to me like > :the check could mess up if uio_offset it right near 0x7fffffffffffffff, > :so that uio->ui_offset + uio->uio_resid ends up negative. I think the > :check a little above that for uio_offset < 0 should also check > :uio_offset + uio_resid < 0 to avoid this. > : > :rick > > Yes, though doing an overflow check in C, at least with newer versions > of GCC, requires a separate comparison. The language has been mangled > pretty badly over the years. > > > if (a + b < a) -> can be optimized-out by the compiler > > if (a + b < 0) -> also can be optimized-out by the compiler > > x = a + b; > if (x < a) -> this is ok (best method) > > x = a + b; > if (x < 0) -> this is ok > > > This sort of check may already be made in various places (e.g. by UFS > and/or uio), since negative offsets are used to identify meta-data in > UFS. > > -Matt > Matthew Dillon > <dillon@backplane.com> my question, badly written, was why not let the underlaying fs (ufs, zfs, etc) have the last word, instead of the nfsclient having to guess? Is there a problem in sending back the error? danny
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