Re: Read/write counts

[Andreas Dilger <adilger@clusterfs.com>]

On Jun 04, 2007  06:20 -0400, David H. Lynch Jr. wrote:
> The net result is that implimentation would be simpler if I could
> just read/write, the amount of data that can be done with the least
> amount of work, even if that is less than was requested.
> 
> If I receive a request to read 512 bytes, and I return that I have read
> 486, is either the OS, libc, or something else going to treat that as an
> error, or are they coming back for the rest in a subsequent call ?
> 
> I though I recalled that read()/write() returning a cound less than
> requested is not an error.

It is not strictly an error to read/write less than the requested amount,
but you will find that a lot of applications don't handle this correctly.
They will assume that if the amount read/written is != amount requested
that this is an error.  Of course the opposite is also true - some
applications assume that the amount requested == amount read/written and
don't even check whether that is actually the case or not.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.