Re: [Qemu-devel] [PATCH v5 4/6] introduce new vma archive format

[Markus Armbruster]

Dietmar Maurer <address@hidden> writes:

> This is a very simple archive format, see docs/specs/vma_spec.txt
>
> Signed-off-by: Dietmar Maurer <address@hidden>
> ---
>  Makefile                |    3 +-
>  Makefile.objs           |    2 +-
>  blockdev.c              |    6 +-
>  docs/specs/vma_spec.txt |   24 ++
>  vma-reader.c            |  799 ++++++++++++++++++++++++++++++++++++++++
>  vma-writer.c            |  940 
> +++++++++++++++++++++++++++++++++++++++++++++++
>  vma.c                   |  561 ++++++++++++++++++++++++++++
>  vma.h                   |  145 ++++++++
>  8 files changed, 2476 insertions(+), 4 deletions(-)
>  create mode 100644 docs/specs/vma_spec.txt
>  create mode 100644 vma-reader.c
>  create mode 100644 vma-writer.c
>  create mode 100644 vma.c
>  create mode 100644 vma.h
>
> diff --git a/Makefile b/Makefile
> index 0d9099a..16f1c25 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -115,7 +115,7 @@ ifeq ($(CONFIG_SMARTCARD_NSS),y)
>  include $(SRC_PATH)/libcacard/Makefile
>  endif
>  
> -all: $(DOCS) $(TOOLS) $(HELPERS-y) recurse-all
> +all: $(DOCS) $(TOOLS) vma$(EXESUF) $(HELPERS-y) recurse-all
>  
>  config-host.h: config-host.h-timestamp
>  config-host.h-timestamp: config-host.mak
> @@ -167,6 +167,7 @@ qemu-img.o: qemu-img-cmds.h
>  qemu-img$(EXESUF): qemu-img.o $(block-obj-y) libqemuutil.a libqemustub.a
>  qemu-nbd$(EXESUF): qemu-nbd.o $(block-obj-y) libqemuutil.a libqemustub.a
>  qemu-io$(EXESUF): qemu-io.o cmd.o $(block-obj-y) libqemuutil.a libqemustub.a
> +vma$(EXESUF): vma.o vma-writer.o vma-reader.o $(block-obj-y)  libqemuutil.a 
> libqemustub.a
>  
>  qemu-bridge-helper$(EXESUF): qemu-bridge-helper.o
>  
> diff --git a/Makefile.objs b/Makefile.objs
> index df64f70..91f133b 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -13,7 +13,7 @@ block-obj-$(CONFIG_POSIX) += aio-posix.o
>  block-obj-$(CONFIG_WIN32) += aio-win32.o
>  block-obj-y += block/
>  block-obj-y += qapi-types.o qapi-visit.o
> -block-obj-y += backup.o
> +block-obj-y += vma-writer.o backup.o
>  
>  block-obj-y += qemu-coroutine.o qemu-coroutine-lock.o qemu-coroutine-io.o
>  block-obj-y += qemu-coroutine-sleep.o
> diff --git a/blockdev.c b/blockdev.c
> index 84f598d..683f7da 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -21,6 +21,7 @@
>  #include "trace.h"
>  #include "sysemu/arch_init.h"
>  #include "backup.h"
> +#include "vma.h"
>  
>  static QTAILQ_HEAD(drivelist, DriveInfo) drives = 
> QTAILQ_HEAD_INITIALIZER(drives);
>  
> @@ -1530,10 +1531,11 @@ char *qmp_backup(const char *backup_file, bool 
> has_format, BackupFormat format,
>      /* Todo: try to auto-detect format based on file name */
>      format = has_format ? format : BACKUP_FORMAT_VMA;
>  
> -    /* fixme: find driver for specifued format */
>      const BackupDriver *driver = NULL;
>  
> -    if (!driver) {
> +    if (format == BACKUP_FORMAT_VMA) {
> +        driver = &backup_vma_driver;
> +    } else {
>          error_set(errp, ERROR_CLASS_GENERIC_ERROR, "unknown backup format");
>          return NULL;
>      }
> diff --git a/docs/specs/vma_spec.txt b/docs/specs/vma_spec.txt
> new file mode 100644
> index 0000000..9b715f2
> --- /dev/null
> +++ b/docs/specs/vma_spec.txt
> @@ -0,0 +1,24 @@
> +=Virtual Machine Archive format (VMA)=
> +
> +This format contains a header which includes the VM configuration as
> +binary blobs, and a list of devices (dev_id, name).
> +
> +The actual VM image data is stored inside extents. An extent contains
> +up to 64 clusters, and start with a 512 byte header containing
> +additional information for those clusters.
> +
> +We use a cluster size of 65536, and use 8 bytes for each
> +cluster in the header to store the following information:
> +
> +* 1 byte dev_id (to identity the drive)
> +* 1 byte not used (reserved)
> +* 2 bytes zero indicator (mark zero regions (16x4096))
> +* 4 bytes cluster number
> +
> +We only store non-zero blocks (such block is 4096 bytes).
> +
> +Each archive is marked with a uuid. The archive header and all
> +extent headers includes that uuid and a MD5 checksum (over header
> +data).
> +
> +

Trailing blank lines.

This isn't a specification, yet.  I'm very much opposed to
underspecified *external* interfaces, because that makes changing
anything without breaking interoperability a crap shot.

We'll review the implementation against the specification as soon as we
got one.

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