Re: Adding read_exact and write_all OPs?

[Stefan Metzmacher <metze@samba.org>]

Hi Jens,

>> In application code it's quite common to write/read a whole buffer and
>> only then continue task execution. The traditional approach is to wrap
>> read/write sycall/OP in loop, which is often done as part of a
>> language std. In synchronous context it makes sense because it allows
>> to process things like EINTR. But in asynchronous (event-driven)
>> context I think it makes a bit less sense.
>>
>> What do you think about potential addition of OPs like read_exact and
>> write_all, i.e. OPs which on successful CQE guarantee that an input
>> buffer was processed completely? They would allow to simplify user
>> code and in some cases to significantly reduce ring traffic.
> 
> That may make sense, and there's some precedence there for sockets with
> the WAITALL flags.

I remember we got short reads/writes from some early kernel versions
and had to add a retry in samba.

But don't we already have a retry in current kernels?
At least for the need_complete_io() case?
io_rw_should_reissue() also seem to be related and also handles S_ISREG,
but it's hidden behind CONFIG_BLOCK.

Are there really systems without CONFIG_BLOCK?

metze