Re: [Qemu-devel] [PATCH qemu] migration/vmstate: document VMStateFlags

[Juan Quintela]

Sascha Silbe <address@hidden> wrote:
> The VMState API is rather sparsely documented. Start by describing the
> meaning of all VMStateFlags.
>
> Signed-off-by: Sascha Silbe <address@hidden>
> ---
> 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 <address@hidden>

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 {