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Added info about v1.1 images
== Images in criu-specific format ==
== Images in criu-specific format ==
All criu-specific image files begin with 32-bit magic cookie. Images in PB format are followed by zero or more entries of the same type (not size!), each entry is preceded with 32-bit entry size value (not including this 32-bit value itself). Optionally each entry may be followed by extra payload which depends on the entry type.
All criu-specific image files begin with 2 32-bit magic cookies. The first cookie is the type of file (see below) the second is the optional sub-type of image. Images in PB format are followed by zero or more entries of the same type (not size!), each entry is preceded with 32-bit entry size value (not including this 32-bit value itself). Optionally each entry may be followed by extra payload which depends on the entry type.
Currently there are 3 types of images
; Inventory file
: This is the image file describing the set. It doesn't have sub-type magic.
; Image file
: Regular image. Most of the text below is about these files.
; Auxiliary file
: File that is not image, but criu generates one and it happens to be in protobuf format too. For now we have only stats and irmap cache files of that type. They also have sub-type magic.
IOW protocol-buffers image files look like
IOW protocol-buffers image files look like
<pre>
<pre>
IMAGE_FILE ::= MAGIC { ENTRY }
IMAGE_FILE ::= MAGIC [MAGIC_2] { ENTRY }
ENTRY ::= SIZE PAYLOAD [ EXTRA ]
ENTRY ::= SIZE PAYLOAD [ EXTRA ]
PAYLOAD ::= "message encoded in ProtocolBuffer format"
PAYLOAD ::= "message encoded in ProtocolBuffer format"
MAGIC ::= "32 bit integer"
MAGIC ::= "32 bit integer"
MAGIC_2 ::= "32 bit integer"
SIZE ::= "32 bit integer, equals the PAYLOAD length"
SIZE ::= "32 bit integer, equals the PAYLOAD length"
</pre>
</pre>