[Libguestfs] [PATCH nbdkit v4 05/15] cow: Disable extents information in this filter.

The cow filter doesn't support trimming and we should assume the underlying plugin is fully allocated too. Note that both of these limitations might be lifted with a more advanced filter implementation. However we ought to support this in future 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, void *handle) @@ -128,6 +128,12 @@ cow_can_trim (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle) return 0; } +static int +cow_can_extents (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle) +{ + return 0; +} + static int cow_can_flush (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle) { @@ -316,6 +322,7 @@ static struct nbdkit_filter filter = { .can_write = cow_can_write, .can_flush = cow_can_flush, .can_trim = cow_can_trim, + .can_extents = cow_can_extents, .can_fua = cow_can_fua, .pread = cow_pread, .pwrite = cow_pwrite, -- 2.20.1