NFS: file too large

[Matthew Dillon]

: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 at backplane.com>