PROBLEM: blocking read on socket repeatedly returns EAGAIN

[Kern Sibbald <kern@sibbald.com>]

A read() on a TCP/IP socket, which should block returns -1 with errno=EAGAIN

Unless I am mistaken, the read() should block as the socket is active with no 
problems.  The only "unusual" items are that I have set the network buffer 
size to 32K (32 * 1024), IPTOS_THROUGHPUT, and keepalive.  In addition, I put 
a lot of data into the write side of the socket, then do the read().  The 
other end of the socket is perfectly alive, but does not read() the data I 
have written, nor does it write() anything.  When my read() is issued, I 
expect it to block, but it immediately returns with -1 and errno set to 
EAGAIN.  If the read() is re-issued, a CPU intensive loop results as long as 
the other end does not read() the data written to the socket.  This is a 
multi-threaded program, but the other threads are all blocked on something.

Kernel: Fedora FC4
Linux version 2.6.12-1.1398_FC4smp (bhcompile@tweety.build.redhat.com) (gcc 
version 4.0.0 20050519 (Red Hat 4.0.0-8)) #1 SMP Fri Jul 15 01:30:13 EDT 2005

This problem occurs in my network backup program, Bacula, so it would be a 
fair amount of work to send you a program that shows this behavior.

Best regards,

Kern