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You're right about EAGAIN. The behavior I mentioned seems to
be valid only for old Unixes, as presented here:

http://www.gnu.org/manual/glibc/html_mono/libc.html

So indeed we should check for both. OTOH, the above URL also
mentions that EAGAIN can happen in blocking situations as well:

"On some systems, reading a large amount of data from a
character special file can also fail with EAGAIN if the
kernel cannot find enough physical memory to lock down the
user's pages."

Also, the statement in the documentation you mention isn't
true even without my patch. We currently check for
"readbytes < requestedbytes" and break the loop if it
happens. Indeed, that's one of the reasons that
created the second problem I've mentioned. Enforcing this
behavior, I could see that mentioned in the URL above:

"Any condition that could result in EAGAIN can instead
result in a successful read which returns fewer bytes than
requested. Calling read again immediately would result in
EAGAIN."

Thusly, applying this patch we wouldn't be introducing a new
behavior, but just enforcing a single behavior in every case.