[patch/rfc] target read/write partial

[Andrew Cagney]

> On Wed, Oct 15, 2003 at 06:16:28PM -0400, Andrew Cagney wrote:
> 
>> Hello,
>> 
>> This patch adds target read/write partial methods.
>> 
>> It's almost ready for prime time.  I want to first see through some 
>> other target cleanups namely:
>> +  /* FIXME: cagney/2003-10-15: This code should walk down the target
>> +     stack looking for a stratum that supports the mechanism.
>> +     Unfortunatly, there isn't a per-target-stack chain to walk round.
>> +     Catch-22.  */
>> and a s/target_ops/target/ transformation.
> 
> 
> Preferably not target - didn't someone suggest gdbtarg?  Or maybe
> gdb_target.

... you mean someone actually likes gdbtarg :-)

>> Note that it includes:
>> +  /* Transfer up-to LEN bytes of memory starting at OFFSET.  */
>> +  TARGET_OBJECT_MEMORY
>> I'm going to need that when implementing a per-target 
>> CONVERT_FROM_FUNC_PTR_ADDR.
> 
> 
> How is that different from a memory read, which we've already got? I am
> guessing that it's because you want to support partial memory
> operations (avoid packet size limits), but you never explained your
> goal.

I previously wrote:

> In the light of Joel's "upload/download" commands, and lessons (gdb/589) learn't from similar interfaces, and a realization that I need this for memory:
...
> - it takes an explicit target vector
> - there are both read and write variants (instead of query)
> - it, what the heck, takes a LONGEST
> - it makes the fact that the method isn't expected to perform a full transfer explicit

gdb/589 is yet another example of how the existing code always did 
partial xfers, yet no one noticed.  Have a look at how many levels of 
GDB code try to locally solve the partial transfer problem when 
generic_load is called.

The only significant difference is the addition of an explicit target 
vector.  But that's really significant.  I should probably comment out 
TARGET_OBJECT_MEMORY until a target implements it.

>> +  /* Map pre-existing objects onto letters.  DO NOT do this for new
>> +     objects!!!  Instead specify new query packets.  */
> 
> 
> Could that be a little clearer - I had to read the code a couple of
> times to figure out what you meant.  I guess you just want to say that
> there's no need to use single letters?

The code abuses:

	<letter> + <annex>

as a way of generating packets.  The entire qK* and qR* packet maps have 
been kidnapped by this.  The un-approved RedBoot patches did the same 
with qM*.

I'll expand the comment.

>> +  /* Minimum outbuf size is (rs->remote_packet_size) - if bufsiz is
>> +     not large enough let the caller.  */
> 
> 
> Missing a word there I think.

Will fix.

Andrew