Couple of questions that might help make my
module a little more sane;
0) Is there any developer docco? I've just done
another quick search and I can't see any. Let
me know if there is and I'll try and answer the
below myself.
1) What is the difference between STACK_WIND
and STACK_WIND_COOKIE? I.e. I've only
ever used STACK_WIND, when should I use
it versus the other?
STACK_WIND_COOKIE is used when we need to 'tie' the call
wound with its corresponding callback. You can see this
variant being used extensively in cluster xlators where it
is used to identify the callback with the subvolume no. it
is coming from.
2) Is there a way to write linearly within a single
function within Gluster (or is there a reason
why I wouldn't want to do that)?
RE 2:
This may stem from my lack of understanding
of the broader Gluster internals. I am performing
multiple fops per fop, which is creating structural
inelegances in the code that make me think I'm
heading down the wrong rabbit hole. I want to
say;
read() {
// pull in other content
while(want more) {
_lookup()
_open()
_read()
_close()
}
return iovec
}
But the way I've understood the Gluster internal
structure is that I need to operate in a chain of
related functions;
_read_lookup_cbk_open_cbk_read_cbk() {
wind _close()
}
_read_lookup_cbk_open_cbk() {
wind _read()
add to local->iovec
}
_lookup_cbk() {
wind _open()
}
read() {
while(want more) {
wind _lookup()
}
return local->iovec
}
Am I missing something - or is there a nicer way of
doing this?
The above method you are trying to use is the "continuation passing style" that
is extensively used in afr-inode-read.c and afr-transaction.c to perform multiple
internal fops on the trigger of a single fop from the application. cluster/afr may
give you some ideas on how you could structure it if you like that more.
The other method I can think of (not sure if it would suit your needs)
is to use the syncop framework (see libglusterfs/src/syncop.c).
This allows one to make a 'synchronous' glusterfs fop. inside a xlator.
The downside is that you can only make one call at a time. This may not
be acceptable for cluster xlators (ie, xlator with more than one child xlator).
Hope that helps,
krish
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