| Message ID | 1453408767-4905-1-git-send-email-silbe@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
On (Thu) 21 Jan 2016 [21:39:27], Sascha Silbe wrote: > The VMState API is rather sparsely documented. Start by describing the > meaning of all VMStateFlags. > > Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com> Thanks, this is much needed. I'm just returning from a long trip, will go through this in a bit. Amit
On (Thu) 21 Jan 2016 [21:39:27], Sascha Silbe wrote: > The VMState API is rather sparsely documented. Start by describing the > meaning of all VMStateFlags. > > Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com> Reviewed-by: Amit Shah <amit.shah@redhat.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. Yes, nice. Thanks! Amit
Sascha Silbe <silbe@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 <silbe@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 <quintela@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 {
On (Thu) 21 Jan 2016 [21:39:27], Sascha Silbe wrote: > The VMState API is rather sparsely documented. Start by describing the > meaning of all VMStateFlags. > > Signed-off-by: Sascha Silbe <silbe@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. Thanks, I've pulled this in my queue. There's one new flag added: VMS_MULTIPLY_ELEMENTS. Do you want to send a follow-up patch to add a description to that one as well? Amit
Dear Amit, Amit Shah <amit.shah@redhat.com> writes: > On (Thu) 21 Jan 2016 [21:39:27], Sascha Silbe wrote: >> The VMState API is rather sparsely documented. Start by describing the >> meaning of all VMStateFlags. > Thanks, I've pulled this in my queue. > > There's one new flag added: VMS_MULTIPLY_ELEMENTS. Do you want to > send a follow-up patch to add a description to that one as well? I can either send a new version with the conflicts resolved and VMS_MULTIPLY_ELEMENTS documented (i.e. rebased on current master), or a follow-up patch with just the differences to your version if you point me at your git repo. Whatever works best for you. Sascha
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 {
The VMState API is rather sparsely documented. Start by describing the meaning of all VMStateFlags. Signed-off-by: Sascha Silbe <silbe@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(-)