ftp.parl.clemson.edu/2015-02-07.ftp.parl.clemson.edu.tar/ftp.parl.clemson.edu/pub/pvfs2/orangefs-2.8.3-20110323.tar.gz/orangefs-2.8.3-20110323.tar/orangefs/src/io/description/usage-notes.txt

Text File | 2003-01-10 | 2KB | 50 lines

creating requests:

requests are created using the request constructor calls
and the predefined requests defined in pvfs_requests.h.

"packing" requests:

can be done two ways.  User function PVFS_Request_commit
allocates new memory and packs the request into it.  internal
function PINT_Request_commit packs into a buffer provided
by the call.  struct PINT_Request structure has a field
named num_nested_req that is the number of struct PINT_Request
structures in the request below (not including) the current one.
This is an upper bound assuming you don't re-pack the same
subtree (which the functions shouldn't do).

encoding/decoding requests:

requests are encoded in place with PINT_Request_encode - copy
first if you want to.  decode function works the same way

processing requests:

to process a request you need a request state structure (which
references a request), and rfdata struct which references a
distribution and has a few key metadata items (number of servers,
server number, file size) plus you need arrays to receive the
offset and length pairs, plus a few arguments.  You can
have multiple states in use simultaneously

creating distributions

users create distributions before creating files with PVFS_Dist_create
These are allocated contiguously in memory, have a private copy
of the default parameters, but no pointer to the methods (users
don't need 'em).  These can be passed to the create system call

encoding/decoding distributions

PINT_Dist_encode can either copy a dist into a provided buffer
or encode in place to avoid a copy. same for decode.

finding methods

PINT_Dist_lookup looks up a distribution and sets up the methods
in the PINT_Dist structure - this should be done before passing
a dist in for processing a request (a future version could do
this automatically).