Re: [Qemu-devel] [PATCH] [RFC] libqblock draft code v1

[Stefan Hajnoczi]

On Wed, Aug 1, 2012 at 10:09 AM, Wenchao Xia <address@hidden> wrote:
>   This patch encapsulate qemu general block layer to provide block
> services. API are declared in libqblock.h. libqblock-test.c
> simulate library consumer's behaviors. Make libqblock-test could
> build the code.
>   For easy this patch does not form a dynamic libarary yet.
>
> Signed-off-by: Wenchao Xia <address@hidden>
> ---
>  Makefile         |    4 +-
>  libqblock-test.c |   56 +++++++++++++++
>  libqblock.c      |  199 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  libqblock.h      |   72 ++++++++++++++++++++
>  4 files changed, 330 insertions(+), 1 deletions(-)
>  create mode 100644 libqblock-test.c
>  create mode 100644 libqblock.c
>  create mode 100644 libqblock.h

I haven't looked at Paolo's feedback yet, so please ignore any
duplicate comments :).

Please include API documentation.  I suggest doc comments in the
libqblock.h header file.

> diff --git a/Makefile b/Makefile
> index 621cb86..6a34be6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -152,7 +152,6 @@ vscclient$(EXESUF): $(libcacard-y) $(oslib-obj-y) 
> $(trace-obj-y) qemu-timer-comm
>         $(call quiet-command,$(CC) $(LDFLAGS) -o $@ $^ $(libcacard_libs) 
> $(LIBS),"  LINK  $@")
>
>  ######################################################################
> -
>  qemu-img.o: qemu-img-cmds.h
>
>  tools-obj-y = $(oslib-obj-y) $(trace-obj-y) qemu-tool.o qemu-timer.o \

Whitespace change.  Please drop this.

> @@ -160,6 +159,9 @@ tools-obj-y = $(oslib-obj-y) $(trace-obj-y) qemu-tool.o 
> qemu-timer.o \
>         iohandler.o cutils.o iov.o async.o
>  tools-obj-$(CONFIG_POSIX) += compatfd.o
>
> +libqblock-test$(EXESUF): libqblock.o libqblock-test.o $(tools-obj-y) 
> $(block-obj-y)
> +       $(call quiet-command,$(CC) $(LDFLAGS) -o $@ $^ $(LIBS),"  LINK  $@")
> +
>  qemu-img$(EXESUF): qemu-img.o $(tools-obj-y) $(block-obj-y)
>  qemu-nbd$(EXESUF): qemu-nbd.o $(tools-obj-y) $(block-obj-y)
>  qemu-io$(EXESUF): qemu-io.o cmd.o $(tools-obj-y) $(block-obj-y)
> diff --git a/libqblock-test.c b/libqblock-test.c
> new file mode 100644
> index 0000000..663111e
> --- /dev/null
> +++ b/libqblock-test.c
> @@ -0,0 +1,56 @@
> +#include "libqblock.h"

Please include GPLv2+ license headers in new source files you create.
See existing code like include/qemu/object.h for the license header
text.

> +
> +#include <stdarg.h>
> +#include <stdio.h>
> +
> +
> +unsigned char buf0[1024];
> +unsigned char buf1[1024] = {4, 0, 0, 2};
> +int main(int argc, char **argv)
> +{
> +    struct QBlockState i_qbs;
> +    struct QBlockOpenOption i_qboo;
> +    struct QBlockCreateOption i_qbco;
> +    struct QBlockInfo i_qbi;

What does i_ mean? :)

> +    char *filename;
> +
> +    int i;
> +    unsigned long op_size = 512;
> +    unsigned long op_start = 1024;
> +
> +    filename = argv[1];
> +    printf("qemu test, file name is %s.\n", filename);
> +
> +    libqblock_init();
> +
> +    qbs_init(&i_qbs);
> +    memset(&i_qbco, 0, sizeof(struct QBlockCreateOption));
> +
> +    i_qbco.filename = filename;
> +    i_qbco.fmt = (char *)"qcow2";

Why does fmt need to be char* and not const char*?

> +    i_qbco.flag = BDRV_O_NOCACHE;

BDRV_O_* constants are not an ABI.  That means they are not stable and
could change (because they are QEMU internals).

Either BDRV_O_* needs to become a public ABI or we need public
constants for libqblock.

> +    i_qbco.size = 512 * 1024 * 1024;
> +    qb_create(&i_qbs, &i_qbco);
> +
> +    i_qboo.filename = filename;
> +    i_qboo.flag = BDRV_O_RDWR;
> +    qb_open(&i_qbs, &i_qboo);

Error handling is worth showing too.

> +
> +    qb_write(&i_qbs, op_start, op_size, buf1);
> +    qb_read(&i_qbs, op_start, op_size, buf0);
> +    for (i = 0; i < op_size; i++) {
> +        if (buf0[i] != buf1[i]) {
> +            printf("unmatch found at %d.\n", i);
> +            break;
> +        }
> +    }
> +    qbi_init(&i_qbi);
> +    qb_getinfo(&i_qbs, &i_qbi);
> +    qbi_print_test(&i_qbi);
> +    qbi_uninit(&i_qbi);
> +
> +    qb_close(&i_qbs);
> +    qb_delete(&i_qbs, filename);
> +    qbs_uninit(&i_qbs);
> +    return 0;
> +}
> diff --git a/libqblock.c b/libqblock.c
> new file mode 100644
> index 0000000..00b6649
> --- /dev/null
> +++ b/libqblock.c
> @@ -0,0 +1,199 @@
> +#include "libqblock.h"
> +
> +#include <unistd.h>
> +
> +#define QB_ERR_MEM_ERR (-1)
> +#define QB_ERR_INTERNAL_ERR (-2)
> +#define QB_ERR_INVALID_PARAM (-3)
> +
> +#define FUNC_FREE g_free
> +
> +#define CLEAN_FREE(p) { \
> +        FUNC_FREE(p); \
> +        (p) = NULL; \
> +}
> +
> +/* try string dup and check if it succeed, dest would be freed before dup */
> +#define SAFE_STRDUP(dest, src, ret, err_v) { \
> +    if ((ret) != (err_v)) { \
> +        if ((dest) != NULL) { \
> +            FUNC_FREE(dest); \
> +        } \
> +        (dest) = strdup(src); \
> +        if ((dest) == NULL) { \
> +            (ret) = (err_v); \
> +        } \
> +    } \
> +}

I'm not a fan of these macros.  Use g_strdup() and don't hide simple
operations like freeing and clearing a pointer.

> +int libqblock_init(void)
> +{
> +    bdrv_init();
> +    return 0;
> +}
> +
> +int qbs_init(struct QBlockState *qbs)
> +{
> +    memset(qbs, 0, sizeof(struct QBlockState));
> +    qbs->bdrvs = bdrv_new("hda");
> +    if (qbs->bdrvs == NULL) {
> +        return QB_ERR_INTERNAL_ERR;
> +    }
> +    return 0;
> +}
> +
> +int qbs_uninit(struct QBlockState *qbs)
> +{
> +    CLEAN_FREE(qbs->filename);
> +    if (qbs->bdrvs == NULL) {
> +        return QB_ERR_INVALID_PARAM;

Being able to safely close/uninitialize/etc an object multiple times
is a useful property.  I would return 0 here instead of an error.

> +    }
> +    bdrv_delete(qbs->bdrvs);
> +    return 0;
> +}
> +
> +int qb_create(struct QBlockState *qbs, struct QBlockCreateOption *op)

Why are some functions called qbs_*() and others qb_*()?

> +{
> +    int ret;
> +    BlockDriverState *bs;
> +
> +    bs = (BlockDriverState *)qbs->bdrvs;

In C casting between void* and another pointer type is implicit and
there is no compiler warning.  Please drop the casts.

I think the easiest way to avoid this type cast issue is to forward
declare "typedef struct BlockDriverState BlockDriverState" in
libqblock.h.  The caller will still be unable to access it directly.

> +
> +    ret = bdrv_img_create(op->filename, op->fmt, op->base_filename,
> +                          op->base_fmt, op->options, op->size, op->flag);
> +    return 0;
> +}
> +
> +int qb_open(struct QBlockState *qbs, struct QBlockOpenOption *op)
> +{
> +    int ret;
> +    BlockDriverState *bs;
> +
> +    bs = (BlockDriverState *)qbs->bdrvs;
> +    ret = bdrv_open(bs, op->filename, op->flag, NULL);
> +    if (ret < 0) {
> +        return ret;

Here you are passing QEMU internal -errno back to the user.  As long
as qb_open() is documented as returning -errno this is okay, but I was
a little surprised because you declared your own error constants for
libqblock.

> +    }
> +
> +    SAFE_STRDUP(qbs->filename, op->filename, ret, QB_ERR_MEM_ERR);
> +    return ret;
> +}
> +
> +int qb_close(struct QBlockState *qbs)
> +{
> +    int ret = 0;
> +    BlockDriverState *bs;
> +
> +    bs = (BlockDriverState *)qbs->bdrvs;
> +    bdrv_close(bs);
> +    return ret;
> +}
> +
> +int qb_delete(struct QBlockState *qbs, const char *filename)
> +{
> +    return unlink(filename);

This is a little tricky.  Some block drivers have no actual file on
disk.  Others use multiple files for a single disk image.

I suggest dropping this API for now.

> +}
> +
> +/* ignore case that len is not alligned to 512 now. */
> +int qb_read(struct QBlockState *qbs, unsigned long start, unsigned long len,
> +                                                          unsigned char *buf)

unsigned long is the wrong type.  It needs to be uint64_t to guarantee 64-bit.

I also suggest using void *buf and size_t len.  This is what the C
standard library APIs use for buffers and sizes.

> +int qbi_init(struct QBlockInfo *info)
> +{
> +    memset(info, 0, sizeof(struct QBlockInfo));
> +    return 0;
> +}

If you think an API will never return an error (even in the future),
then make it return void.  Otherwise all callers have to check the
return value.

> +
> +int qbi_uninit(struct QBlockInfo *info)
> +{
> +    CLEAN_FREE(info->filename);
> +    CLEAN_FREE(info->fmt);
> +    CLEAN_FREE(info->backing_filename);
> +    CLEAN_FREE(info->sn_tab);
> +    return 0;
> +}
> +
> +int qbi_print_test(struct QBlockInfo *info)
> +{
> +    printf("name:%s, fmt %s, virt_size %ld, allocated_size %ld, encryt %d, "
> +           "back_file %s, sn_tab %p, sn_num %d, cluster size %d, "
> +           "vm_state_offset %ld, dirty %d.\n",

Disk offsets and size need to be uint64_t with %PRIu64 format string specifiers.

Stefan