On Wed, Feb 21, 2024 at 4:26 PM Markus Armbruster <arm...@redhat.com> wrote:
> Yong Huang <yong.hu...@smartx.com> writes: > > > On Wed, Feb 21, 2024 at 2:43 PM Markus Armbruster <arm...@redhat.com> > wrote: > > > >> Hyman Huang <yong.hu...@smartx.com> writes: > >> > >> > Add comment in detail for commit 433957bb7f (qapi: > >> > Make parameter 'file' optional for > >> > BlockdevCreateOptionsLUKS). > >> > > >> > Signed-off-by: Hyman Huang <yong.hu...@smartx.com> > >> > --- > >> > qapi/block-core.json | 20 +++++++++++++++++++- > >> > 1 file changed, 19 insertions(+), 1 deletion(-) > >> > > >> > diff --git a/qapi/block-core.json b/qapi/block-core.json > >> > index ab5a93a966..42b0840d43 100644 > >> > --- a/qapi/block-core.json > >> > +++ b/qapi/block-core.json > >> > @@ -4973,7 +4973,25 @@ > >> > ## > >> > # @BlockdevCreateOptionsLUKS: > >> > # > >> > -# Driver specific image creation options for LUKS. > >> > +# Driver specific image creation options for LUKS. Note that > >> > +# @file is required if @preallocation is specified and equals > >> > +# PREALLOC_MODE_ON. The following three scenarios determine how > >> > +# creation logic behaves when @preallocation is either equal to > >> > +# PREALLOC_MODE_OFF or is not given: > >> > +# > >> > +# 1) When @file is given only, format the block device referenced > >> > +# by @file as the LUKS specification and trunk it to the @size. > >> > >> Do you mean "truncate it to @size"? > >> > > Yes, :( sorry for the spelling mistake. > > Writing good documentation in a second language is *hard*. All we can > reasonably expect from contributors to try their best. And then we > improve the text together in review. Just like we do for code :) > > >> > +# In this case, the @size should reflect amount of space made > >> > +# available to the guest, so the trunk size must take account > >> > +# of that which will be used by the crypto header. > >> > +# > >> > +# 2) When @header is given only, just format the block device > >> > +# referenced by @header as the LUKS specification. > >> > +# > >> > +# 3) When both @file and @header are given, block device > >> > +# referenced by @file should be trunked to @size, and block > >> > +# device referenced by @header should be formatted as the LUKS > >> > +# specification. > >> > # > >> > # @file: Node to create the image format on, mandatory except when > >> > # 'preallocation' is not requested > >> > >> Let's see whether I understand. > >> > >> blockdev-create with "driver": "luks" can work in three different ways: > >> > >> 1. Create an image with a LUKS header > >> > >> 2. Create just a detached LUKS header > >> > >> 3. Create an image and a detached LUKS header > >> > >> Correct? > >> > > > > Yes > > > > > >> @file and @header are BlockdevRef, which means they refer to existing > >> images with arbitrary driver. Could be "file", "qcow2", or anything. > >> > >> Correct? > >> > > Yes > > > > > >> > >> To get 1., specify @file, but not @header. > >> > >> To get 2., specify @header, but not @file. > >> > >> To get 3., specify both. > >> > >> Specifying neither is an error. > >> > >> Correct? > >> > > > > Yes > > > > > >> In any case, @size is the logical size of the image (how much data it > >> can hold). > >> > > > > Yes > > > > > >> > >> With 1., the actual image size is a bit larger due to the LUKS header. > >> The @file image is resized to that size: if it's shorter, it's grown, if > >> it's longer, it's truncated. > >> > > > > Yes > > > > > >> With 2., @size is merely recorded in the detached LUKS header. > >> > > > > In LUKS1 specification, payload data size is not contained in the header, > > so in this case, @size is not recorded in the detached LUKS header. > > The creation logic just does the LUKS header formatting only. > > Is @size unused then? > IIUC, yes. Creation logic will ignore the @size. See the following code in function block_crypto_co_create_luks: if (luks_opts->header) { /* LUKS volume with detached header */ hdr_bs = bdrv_co_open_blockdev_ref(luks_opts->header, errp); if (hdr_bs == NULL) { return -EIO; } cflags |= QCRYPTO_BLOCK_CREATE_DETACHED; /* Format the LUKS header node, here just ignore the size * and passed zero to block_crypto_co_create_generic */ ret = block_crypto_co_create_generic(hdr_bs, 0, &create_opts, PREALLOC_MODE_OFF, cflags, errp); if (ret < 0) { goto fail; } /* Format the LUKS payload node */ if (luks_opts->file) { ret = block_crypto_co_format_luks_payload(luks_opts, errp); if (ret < 0) { goto fail; } } > > >> With 3., @size is recorded in the detached LUKS header, and the @file > >> image is resized as with 1. > >> > > > > Same reason as above, @size is not recorded and @file image is > > resized to @size exactly. > > > > > >> > >> Correct? > >> > >> > > Thanks for the comment, > > > > Yong > > -- Best regards