Sascha Silbe <si...@linux.vnet.ibm.com> wrote:
> The VMState API is rather sparsely documented. Start by describing the
> meaning of all VMStateFlags.
>
> Signed-off-by: Sascha Silbe <si...@linux.vnet.ibm.com>
> ---
> Since I had to dive into the code for debugging the migration breakage
> anyway, I figured I could just as well write down the result in the
> form of comments so the next one trying to make some sense out of it
> will have a better start.
>
> This is based on my understanding of the code, not necessarily what
> the original author(s) intended.
>
> include/migration/vmstate.h | 93
> ++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 84 insertions(+), 9 deletions(-)
>
Reviewed-by: Juan Quintela <quint...@redhat.com>
Thanks very much
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index 97d44d3..b1bbf68 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -88,20 +88,95 @@ struct VMStateInfo {
> };
>
> enum VMStateFlags {
> + /* Ignored */
> VMS_SINGLE = 0x001,
> +
> + /* The struct member at opaque + VMStateField.offset is a pointer
> + * to the actual field (e.g. struct a { uint8_t *b;
> + * }). Dereference the pointer before using it as basis for
> + * further pointer arithmetic (see e.g. VMS_ARRAY). Does not
> + * affect the meaning of VMStateField.num_offset or
> + * VMStateField.size_offset; see VMS_VARRAY* and VMS_VBUFFER for
> + * those. */
> VMS_POINTER = 0x002,
> +
> + /* The field is an array of fixed size. VMStateField.num contains
> + * the number of entries in the array. The size of each entry is
> + * given by VMStateField.size and / or opaque +
> + * VMStateField.size_offset; see VMS_VBUFFER and
> + * VMS_MULTIPLY. Each array entry will be processed individually
> + * (VMStateField.info.get()/put() if VMS_STRUCT is not set,
> + * recursion into VMStateField.vmsd if VMS_STRUCT is set). May not
> + * be combined with VMS_VARRAY*. */
> VMS_ARRAY = 0x004,
> +
> + /* The field is itself a struct, containing one or more
> + * fields. Recurse into VMStateField.vmsd. Most useful in
> + * combination with VMS_ARRAY / VMS_VARRAY*, recursing into each
> + * array entry. */
> VMS_STRUCT = 0x008,
> - VMS_VARRAY_INT32 = 0x010, /* Array with size in int32_t field*/
> - VMS_BUFFER = 0x020, /* static sized buffer */
> +
> + /* The field is an array of variable size. The int32_t at opaque +
> + * VMStateField.num_offset contains the number of entries in the
> + * array. See the VMS_ARRAY description regarding array handling
> + * in general. May not be combined with VMS_ARRAY or any other
> + * VMS_VARRAY*. */
> + VMS_VARRAY_INT32 = 0x010,
> +
> + /* Ignored */
> + VMS_BUFFER = 0x020,
> +
> + /* The field is a (fixed-size or variable-size) array of pointers
> + * (e.g. struct a { uint8_t *b[]; }). Dereference each array entry
> + * before using it. Note: Does not imply any one of VMS_ARRAY /
> + * VMS_VARRAY*; these need to be set explicitly. */
> VMS_ARRAY_OF_POINTER = 0x040,
> - VMS_VARRAY_UINT16 = 0x080, /* Array with size in uint16_t field */
> - VMS_VBUFFER = 0x100, /* Buffer with size in int32_t field */
> - VMS_MULTIPLY = 0x200, /* multiply "size" field by field_size */
> - VMS_VARRAY_UINT8 = 0x400, /* Array with size in uint8_t field*/
> - VMS_VARRAY_UINT32 = 0x800, /* Array with size in uint32_t field*/
> - VMS_MUST_EXIST = 0x1000, /* Field must exist in input */
> - VMS_ALLOC = 0x2000, /* Alloc a buffer on the destination */
> +
> + /* The field is an array of variable size. The uint16_t at opaque
> + * + VMStateField.num_offset contains the number of entries in the
> + * array. See the VMS_ARRAY description regarding array handling
> + * in general. May not be combined with VMS_ARRAY or any other
> + * VMS_VARRAY*. */
> + VMS_VARRAY_UINT16 = 0x080,
> +
> + /* The size of the individual entries (a single array entry if
> + * VMS_ARRAY or VMS_VARRAY are set, or the field itself if neither
> + * is set) is variable (i.e. not known at compile-time), but the
> + * same for all entries. Use the int32_t at opaque +
> + * VMStateField.size_offset (subject to VMS_MULTIPLY) to determine
> + * the size of each (and every) entry. */
> + VMS_VBUFFER = 0x100,
> +
> + /* Multiply the entry size given by the int32_t at opaque +
> + * VMStateField.size_offset (see VMS_VBUFFER description) with
> + * VMStateField.size to determine the number of bytes to be
> + * allocated. Only valid in combination with VMS_VBUFFER. */
> + VMS_MULTIPLY = 0x200,
> +
> + /* The field is an array of variable size. The uint8_t at opaque +
> + * VMStateField.num_offset contains the number of entries in the
> + * array. See the VMS_ARRAY description regarding array handling
> + * in general. May not be combined with VMS_ARRAY or any other
> + * VMS_VARRAY*. */
> + VMS_VARRAY_UINT8 = 0x400,
> +
> + /* The field is an array of variable size. The uint32_t at opaque
> + * + VMStateField.num_offset contains the number of entries in the
> + * array. See the VMS_ARRAY description regarding array handling
> + * in general. May not be combined with VMS_ARRAY or any other
> + * VMS_VARRAY*. */
> + VMS_VARRAY_UINT32 = 0x800,
> +
> + /* Fail loading the serialised VM state if this field is missing
> + * from the input. */
> + VMS_MUST_EXIST = 0x1000,
> +
> + /* When loading serialised VM state, allocate memory for the
> + * (entire) field. Only valid in combination with
> + * VMS_POINTER. Note: Not all combinations with other flags are
> + * currently supported, e.g. VMS_ALLOC|VMS_ARRAY_OF_POINTER won't
> + * cause the individual entries to be allocated. */
> + VMS_ALLOC = 0x2000,
> };
>
> typedef struct {
