Read/write counts

["David H. Lynch Jr." <dhlii@comcast.net>]

    I have a file system that has really odd blocking.

    All files have a variable length header (basically a directory
entry) at their start.
    Most but not all sectors, have a small fixed length signature as
well as some link data at their start.

    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.