Il 09/08/2012 12:12, Wenchao Xia ha scritto:
> +/* copy information and take care the member difference in differect version.
> + Assuming all new member are added in the tail, struct size is the first
> + member, this is old to new version, src have its struct_size set. */
> +static void qboc_adjust_o2n(struct QBlockOptionCreate *dest,
> + struct QBlockOptionCreate *src)
> +{
> + /* for simple it does memcpy now, need to take care of embbed structure
> */
> + memcpy(dest, src, src->struct_size);
You need an assertion that src->struct_size < sizeof(*dest).
However, the structure size perhaps wasn't my brightest idea ever. But
still thanks for preparing this prototype! Now that we have a more
complete API to discuss, we can iterate to something better.
> + assert(0 == set_option_parameter_int(param,
> + BLOCK_OPT_SIZE, o_cow->virt_size));
Assertions should not have side effects.
> diff --git a/libqblock.h b/libqblock.h
> new file mode 100644
> index 0000000..d2e9502
> --- /dev/null
> +++ b/libqblock.h
> @@ -0,0 +1,447 @@
> +/*
> + * Copyright IBM Corp. 2012
> + *
> + * Authors:
> + * Wenchao Xia <xiaw...@linux.vnet.ibm.com>
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
> + */
> +
> +#ifndef LIBQBLOCK_H
> +#define LIBQBLOCK_H
> +
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <stdlib.h>
> +
> +#define bool _Bool
> +
> +#define QB_ERR_MEM_ERR (-1)
> +#define QB_ERR_INTERNAL_ERR (-2)
> +#define QB_ERR_INVALID_PARAM (-3)
> +
> +/* this library is designed around this core struct. */
> +struct QBlockState;
> +
> +/*
> + libarary init
> + This function get the library ready to use.
> + */
> +void libqblock_init(void);
> +
> +/*
> + create a new qbs object
> + params:
> + qbs: out, pointer that will receive created obj.
> + return:
> + 0 on succeed, negative on failure.
> + */
> +int qb_state_new(struct QBlockState **qbs);
> +
> +/*
> + delete a qbs object
> + params:
> + qbs: in, pointer that will be freed. *qbs will be set to NULL.
> + return:
> + void.
> + */
> +void qb_state_free(struct QBlockState **qbs);
> +
> +
> +/* flag used in open and create */
> +#define LIBQBLOCK_O_RDWR 0x0002
> +/* open the file read only and save writes in a snapshot */
> +#define LIBQBLOCK_O_SNAPSHOT 0x0008
I'd rather avoid exposing this for now.
> +/* do not use the host page cache */
> +#define LIBQBLOCK_O_NOCACHE 0x0020
> +/* use write-back caching */
> +#define LIBQBLOCK_O_CACHE_WB 0x0040
> +/* use native AIO instead of the thread pool */
> +#define LIBQBLOCK_O_NATIVE_AIO 0x0080
NATIVE_AIO should be an option for the file protocol. But it's mostly
for performance and since we only support synchronous I/O we can drop it
for now.
> +/* don't open the backing file */
> +#define LIBQBLOCK_O_NO_BACKING 0x0100
> +/* disable flushing on this disk */
> +#define LIBQBLOCK_O_NO_FLUSH 0x0200
> +/* copy read backing sectors into image */
> +#define LIBQBLOCK_O_COPY_ON_READ 0x0400
I'd rather avoid exposing this for now too.
> +/* consistency hint for incoming migration */
> +#define LIBQBLOCK_O_INCOMING 0x0800
This is internal to QEMU.
Please add a mask of valid bits and an assertion that unknown bits are zero.
> +
> +#define LIBQBLOCK_O_CACHE_MASK \
> + (LIBQBLOCK_O_NOCACHE | LIBQBLOCK_O_CACHE_WB | LIBQBLOCK_O_NO_FLUSH)
> +
> +enum QBlockProtocol {
> + QB_PROTO_FILE = 0,
> + QB_PROTO_MAX
> +};
> +
> +enum QBlockFormat {
> + QB_FMT_NONE = 0,
> + QB_FMT_COW,
> + QB_FMT_QED,
> + QB_FMT_QCOW,
> + QB_FMT_QCOW2,
> + QB_FMT_RAW,
> + QB_FMT_RBD,
> + QB_FMT_SHEEPDOG,
> + QB_FMT_VDI,
> + QB_FMT_VMDK,
> + QB_FMT_VPC,
> + QB_FMT_MAX
> +};
> +
> +/* block target location info, it include all information about how to find
> + the image */
> +struct QBlockLocInfo {
> + int struct_size;
> + const char *filename;
> + enum QBlockProtocol protocol;
> +};
> +
> +/* how to open the image */
> +struct QBlockOptionOpen {
> + int struct_size;
> + struct QBlockLocInfo o_loc; /* how to find */
> + enum QBlockFormat o_fmt_type; /* how to extract */
> + int o_flag; /* how to control */
> +};
You are right that the embedded structs are very complicated. I think
we need to find the right balance between structs for extensibility and
function arguments for ease of use.
For example, we could have
int qb_open(struct QBlockState *qbs,
struct QBlockLocation *loc,
struct QBlockFormatOption *op,
int o_flag);
where:
- QBlockLocation is basically your QBlockLocInfo, but restructured to
use unions for the protocol-specific fields.
- QBlockFormatOption is basically your QBlockOptionFormat struct. Thus
we can plan for specifying format-specific options at open time rather
than just at create time (this can be useful, for example, for things
such as lazy_refcounts). Until support is there in the block layer, we
can simply check that all format-specific options are zero.
Since both QBlockLocation and QBlockFormatOption are basically a
discriminated record (enum + union of structs) we can add a large char
member to the union (e.g. char padding[512]) to keep the ABI stable.
Users must zero out all fields, and future additions must ensure that
the default value is represented by all-zeros.
> + const char *prealloc_mode; /* off or metadata */
Make this an enum.
> + bool prealloc_mode;
Here too.
> +};
> +
> +struct QBlockOption_vmdk {
> + int struct_size;
> + size_t virt_size;
> + const char *backing_file;
> + int backing_flag;
> + bool compat_version6;
> + const char *subfmt;
> + /* vmdk flat extent format, values:
> + "{monolithicSparse (default) | monolithicFlat | twoGbMaxExtentSparse |
> + twoGbMaxExtentFlat | streamOptimized} */
Here too.
> +/* information */
> +/* image related info, static information, from user perspective. */
> +/* now it is a plain structure, wonder if it could be foldered into embbed
> one
> + to reflect that format related information better. */
> +struct QBlockInfoImage {
QBlockImageInfo
> + int struct_size;
Here the struct size makes more sense, because it's a returned struct.
> + char *filename;
> + enum QBlockProtocol protocol;
Can this just be a struct QBlockLocation * (using a pointer avoids
problems with embedded structs)?
> + enum QBlockFormat format;
Can this just be a struct QBlockFormatOption * (same as the above)?
> + size_t virt_size;
> + /* advance info */
> + size_t allocated_size;
> + bool encrypt;
> + char *backing_filename;
> +};
> +
> +/* image info */
> +/*
> + get image info.
> + params:
> + qbs: in, pointer to QBlockState.
> + info, out, pointer that would receive the information.
> + return:
> + negative on fail, 0 on success.
> + */
> +int qb_infoimage_get(struct QBlockState *qbs, struct QBlockInfoImage **info);
qb_get_image_info
> +
> +/*
> + free image info.
> + params:
> + info, in, pointer, *info would be set to NULL after function called.
> + return:
> + void.
> + */
> +void qb_infoimage_free(struct QBlockInfoImage **info);
qb_free_image_info
Paolo
> +
> +/* misc */
> +bool qb_supports_format(enum QBlockFormat fmt);
> +bool qb_supports_protocol(enum QBlockProtocol proto);
> +
> +const char *qb_error_get_detail(struct QBlockState *qbs, int *err_num);
> +#endif
>
