search for: nbd_init_zero

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...

..., Feb 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...

...t (NBD_INIT_ALL_SPARSE or > >something) that says "the whole image is sparse". Otherwise, I think we > >should redefine NBD_INIT_SPARSE to say that. > > Okay, in v2, I will start with just two bits, NBD_INIT_SPARSE > (entire image is sparse, nothing is allocated) and NBD_INIT_ZERO > (entire image reads as zero), and save any future bits for later > additions. Do we think that 16 bits is sufficient for the amount of > initial information likely to be exposed? So as I understand the proposal, the 16 bit limit comes about because we want a round 4 byte reply, 16 bits...

Hi, On Mon, Feb 10, 2020 at 10:52:55PM +0000, Richard W.M. Jones wrote: > But anyway ... could a flag indicating that the whole image is sparse > be useful, either as well as NBD_INIT_SPARSE or instead of it? You > could use it to avoid an initial disk trim, which is something that > mke2fs does: Yeah, I think that could definitely be useful. I honestly can't see a use for

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 really mean the whole image is s...

...g to say these are always true, but then I remembered that NBD_INIT_* records the state at the start of the *connection*, not the start of the *server* instance, and if there's been a previous connection then the RAM disk might indeed contain non-zero non-sparse data. Do we need to define what NBD_INIT_ZERO means when disk size = 0 ? By the way, the data plugin can also be updated since it also uses the sparse array feature. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists dis...

...en just add a third bit (NBD_INIT_ALL_SPARSE or > something) that says "the whole image is sparse". Otherwise, I think we > should redefine NBD_INIT_SPARSE to say that. Okay, in v2, I will start with just two bits, NBD_INIT_SPARSE (entire image is sparse, nothing is allocated) and NBD_INIT_ZERO (entire image reads as zero), and save any future bits for later additions. Do we think that 16 bits is sufficient for the amount of initial information likely to be exposed? Are we in agreement that my addition of an NBD_INFO_ response to NBD_OPT_GO is the best way to expose initial state b...

...d; Closed ]; + 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...

...ing 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...

The NBD protocol is adding an extension to let servers advertise initialization state to the client: whether the image contains holes, and whether it is known to read as all zeroes. For memory-based plugins, it is fairly easy to advertise several cases: data and memory are usually sparse and detecting zero is easy (requires new functions to the sparse_array common code), although since the sparse