search for: cow_prepar

...because xz files contain sparseness information, so add a note. --- filters/cow/cow.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/filters/cow/cow.c b/filters/cow/cow.c index b8f08c4..570a65f 100644 --- a/filters/cow/cow.c +++ b/filters/cow/cow.c @@ -114,7 +114,7 @@ cow_prepare (struct nbdkit_next_ops *next_ops, void *nxdata, } /* Whatever the underlying plugin can or can't do, we can write, we - * cannot trim, and we can flush. + * cannot trim or detect extents, and we can flush. */ static int cow_can_write (struct nbdkit_next_ops *next_ops, void *nxdata, vo...

...(size == -1) + return -1; + + if (ftruncate (fd, size) == -1) + return -1; + + nbdkit_debug ("cow: underlying file size: %" PRIi64, size); + + return size; +} + +/* Force an early call to cow_get_size, consequently truncating the + * overlay to the correct size. + */ +static int +cow_prepare (struct nbdkit_next_ops *next_ops, void *nxdata, + void *handle) +{ + int64_t r; + + r = cow_get_size (next_ops, nxdata, handle); + return r >= 0 ? 0 : -1; +} + +/* Whatever the underlying plugin can or can't do, we can write, we + * cannot trim, and we can flush. + */ +stati...

Eric, you'll probably find the design "interesting" ... It does work, for me at least. Rich.

...7,7 @@ cow_get_size (struct nbdkit_next_ops *next_ops, void *nxdata, return size; } -/* Force an early call to cow_get_size, consequently truncating the +/* Force early calls to populate nbdkit's cache, and truncate the * overlay to the correct size. */ static int @@ -137,7 +137,14 @@ cow_prepare (struct nbdkit_next_ops *next_ops, void *nxdata, int64_t r; r = cow_get_size (next_ops, nxdata, handle); - return r >= 0 ? 0 : -1; + if (r == -1) + return -1; + + r = next_ops->can_cache (nxdata); + if (r == -1) + return -1; + + return 0; } /* Whatever the underlying plu...

I'm not sure exactly which version we're up to, but let's say it's version 4. I'm a lot happier with this version: - all filters have been reviewed and changed where I think that's necessary - can_extents is properly defined and implemented now - NBD protocol is followed - I believe it addresses all previous review points where possible The "only" thing

Since v1: - rework .can_cache to be tri-state, with default of no advertisement (ripple effect through other patches) - add a lot more patches in order to round out filter support And in the meantime, Rich pushed NBD_CMD_CACHE support into libnbd, so in theory we now have a way to test cache commands through the entire stack. Eric Blake (24): server: Internal hooks for implementing

This has already been pushed upstream. I am simply posting these here so we have a reference in the mailing list in case we find bugs later (as I'm sure we will - it's a complex patch series). Great thanks to Eric Blake for tireless review on this one. It also seems to have identified a few minor bugs in qemu along the way. Rich.

It's easy to use the sh script to demonstrate that nbdkit is inefficiently calling into .get_size, .can_fua, and friends more than necessary. We've also commented on the list in the past that it would be nice to ensure that when filters call into next_ops, they are not violating constraints (as we've have to fix several bugs in the past where we did not have such checking to protect