On Tue, Jul 24, 2007 at 04:34:36PM +0530, Girish Shilamkar wrote:
>
> +struct struct_io_stats {
> + unsigned long long reads;
> + unsigned long long writes;
> +};
I'd suggest doing something like this instead:
struct struct_io_stats {
int num_fields;
int reserved;
unsigned long long bytes_read;
unsigned long long bytes_written;
};
There are other statistics that you might want to gather. For
example, "read_requests" and "write_requests". Or perhaps some
statistics based on discontiguous read/writes (i.e., i/o operations
that cause seeks). Also, in the future we might want to add some kind
of readahead functionality, and that would probably require more
statistics as well.
> + memset(&track->io_start, 0, sizeof(struct struct_io_stats));
> + if (channel && channel->manager && channel->manager->get_stats)
> + channel->manager->get_stats(channel, &track->io_start);
> }
If you're going to use a caller allocates paradigm, then the caller
would be responsible for doing this:
track->io_start.num_fields = 2;
... so the library routine knows how much of the structure it is safe
for it to fill in. Alternatively, it might be easier to simply have
the io_manager pass back a pointer to its own stats structure, and
then the caller would use the num_fields_size to figure out how much
of the structure it can trust.
- Ted
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