Re: TCP hangs in 2.4 - blocking write() in wait_for_tcp_memory

[bert hubert <ahu@ds9a.nl>]

On Wed, Oct 30, 2002 at 10:44:20AM +0000, Miquel van Smoorenburg wrote:

> This makes both socket programs hang in write(), in wait_for_tcp_memory.
> Shouldn't the kernel return a short write, instead of hanging
> both processes ? select() returned writeability.

write(2) is allowed to do a short write on a blocking socket, but not
mandated to do so. In fact I've only seen short writes under
linux on non-blocking sockets.

SuSv3 says:

 Blocking/immediate: Blocking is only possible with O_NONBLOCK clear. If
 there is enough space for all the data requested to be written immediately,
 the implementation should do so. Otherwise, the process may block; that is,
 pause until enough space is available for writing. The effective size of a
 pipe or FIFO (the maximum amount that can be written in one operation
 without blocking) may vary dynamically, depending on the implementation, so
 it is not possible to specify a fixed value for it.

...

 Partial and deferred writes are only possible with O_NONBLOCK set.

Regards,

bert

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