search for: init_zero

...rn if extents are supported; a slight tweak to remember if that result is EOF tells us if we are sparse, and a similar lseek(SEEK_DATA) returning ENXIO tells us if the entire file is a hole, with at most two lseek calls during open (rather than one lseek for each of .can_extents, .init_sparse, and .init_zero). The split plugin is similar to file. For partitioning and linuxdisk, we know we are exposing a sparse image. For other file-based plugins, like ext2, we do not yet expose .extents so it is not worth trying to expose .init_sparse or .init_zero. A successful test depends on whether the current f...

...all four series posted in tandem it becomes easier to see whether any such tweaks are warranted, and can keep such tweaks interoperable before any of the projects land the series upstream]. For now, only 2 of those 16 bits are defined: NBD_INIT_SPARSE (the image has at least one hole) and NBD_INIT_ZERO (the image reads completely as zero); the two bits are orthogonal and can be set independently, although it is easy enough to see completely sparse files with both bits set. Also, advertising the bits is orthogonal to whether the base:allocation metacontext is used, although a server with all...

...ed, 123 insertions(+), 19 deletions(-) diff --git a/docs/nbdkit-filter.pod b/docs/nbdkit-filter.pod index 55dfab1..0f81684 100644 --- a/docs/nbdkit-filter.pod +++ b/docs/nbdkit-filter.pod @@ -413,6 +413,10 @@ cached value. =head2 C<.can_cache> +=head2 C<.init_sparse> + +=head2 C<.init_zero> + int (*can_write) (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle); int (*can_flush) (struct nbdkit_next_ops *next_ops, void *nxdata, @@ -434,6 +438,10 @@ cached value. void *handle); int (*can_cache) (struct nbdkit_next_ops *nex...

...is called during the option negotiation phase to find out if the +plugin knows whether the image starts out as sparse (that is, at least +one unallocated hole, regardless of what might be read from that hole). + +This callback is not required. If omitted, then we return C<0>. + +=head2 C<.init_zero> + + int init_zero (void *handle); + +This is called during the option negotiation phase to find out if the +plugin knows whether the image starts out reading entirely as zero +(regardless of whether the image is sparse). This bit of information +is most useful to a client that plans to copy an...

On 2/10/20 4:12 PM, Richard W.M. Jones wrote: > On Mon, Feb 10, 2020 at 03:37:20PM -0600, Eric Blake wrote: >> For now, only 2 of those 16 bits are defined: NBD_INIT_SPARSE (the >> image has at least one hole) and NBD_INIT_ZERO (the image reads >> completely as zero); the two bits are orthogonal and can be set >> independently, although it is easy enough to see completely sparse >> files with both bits set. > > I think I'm confused about the exact meaning of NBD_INIT_SPARSE. Do > you reall...

...b 10, 2020 at 04:29:53PM -0600, Eric Blake wrote: > On 2/10/20 4:12 PM, Richard W.M. Jones wrote: > >On Mon, Feb 10, 2020 at 03:37:20PM -0600, Eric Blake wrote: > >>For now, only 2 of those 16 bits are defined: NBD_INIT_SPARSE (the > >>image has at least one hole) and NBD_INIT_ZERO (the image reads > >>completely as zero); the two bits are orthogonal and can be set > >>independently, although it is easy enough to see completely sparse > >>files with both bits set. > > > >I think I'm confused about the exact meaning of NBD_INIT_SPARSE...

On Mon, Feb 10, 2020 at 03:43:58PM -0600, Eric Blake wrote: > @@ -214,6 +217,52 @@ file_open (int readonly) > h->can_fallocate = true; > h->can_zeroout = h->is_block_device; > > + h->can_extents = false; > + h->init_sparse = false; > + h->init_zero = false; > +#ifdef SEEK_HOLE > + if (!h->is_block_device) { > + off_t r; > + > + /* A simple test to see whether SEEK_DATA/SEEK_HOLE are likely to work on > + * the current filesystem, and to see if the image is sparse or zero. > + */ > + ACQUIRE_LOCK_FO...

...int i = 0; + +#if LIBNBD_HAVE_NBD_GET_INIT_FLAGS + i = nbd_get_init_flags (h->nbd); + + if (i == -1) { + nbdkit_error ("failure to check init flags: %s", nbd_get_error ()); + return -1; + } + i = !!(i & LIBNBD_INIT_SPARSE); +#endif + return i; +} + +static int +nbdplug_init_zero (void *handle) +{ + struct handle *h = handle; + int i = 0; + +#if LIBNBD_HAVE_NBD_GET_INIT_FLAGS + i = nbd_get_init_flags (h->nbd); + + if (i == -1) { + nbdkit_error ("failure to check init flags: %s", nbd_get_error ()); + return -1; + } + i = !!(i & LIBNBD_INIT_ZERO);...

...losed ]; + shortdesc = "return any init state flags advertised by the server"; + longdesc = "\ +Return the bitwise-OR of any initial state flags advertised by the +server. These flags may include C<LIBNBD_INIT_SPARSE> if the export +is not fully allocated, or C<LIBNBD_INIT_ZERO> if the export is known +to start with all contents reading as zeroes. Other flags might be +added in the future. + +Note that the flags advertised by the server refer only to the point +in time when the connection was established; libnbd does not track if +the results may have been rendered st...