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block/blkio: fix module_block.py parsing
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When QEMU is built with --enable-modules, the module_block.py script
parses block/*.c to find block drivers that are built as modules. The
script generates a table of block drivers called block_driver_modules[].
This table is used for block driver module loading.

The blkio.c driver uses macros to define its BlockDriver structs. This
was done to avoid code duplication but the module_block.py script is
unable to parse the macro. The result is that libblkio-based block
drivers can be built as modules but will not be found at runtime.

One fix is to make the module_block.py script or build system fancier so
it can parse C macros (e.g. by parsing the preprocessed source code). I
chose not to do this because it raises the complexity of the build,
making future issues harder to debug.

Keep things simple: use the macro to avoid duplicating BlockDriver
function pointers but define .format_name and .protocol_name manually
for each BlockDriver. This way the module_block.py is able to parse the
code.

Also get rid of the block driver name macros (e.g. DRIVER_IO_URING)
because module_block.py cannot parse them either.

Fixes: fd66dbd ("blkio: add libblkio block driver")
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20230704123436.187761-1-stefanha@redhat.com
Cc: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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@stefanhaRH
stefanhaRH committed Jul 4, 2023
1 parent d145c0d commit c21eae1
Showing 1 changed file with 60 additions and 56 deletions.
116 changes: 60 additions & 56 deletions block/blkio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,16 +22,6 @@

#include "block/block-io.h"

/*
* Keep the QEMU BlockDriver names identical to the libblkio driver names.
* Using macros instead of typing out the string literals avoids typos.
*/
#define DRIVER_IO_URING "io_uring"
#define DRIVER_NVME_IO_URING "nvme-io_uring"
#define DRIVER_VIRTIO_BLK_VFIO_PCI "virtio-blk-vfio-pci"
#define DRIVER_VIRTIO_BLK_VHOST_USER "virtio-blk-vhost-user"
#define DRIVER_VIRTIO_BLK_VHOST_VDPA "virtio-blk-vhost-vdpa"

/*
* Allocated bounce buffers are kept in a list sorted by buffer address.
*/
Expand Down Expand Up @@ -744,15 +734,15 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
return ret;
}

if (strcmp(blkio_driver, DRIVER_IO_URING) == 0) {
if (strcmp(blkio_driver, "io_uring") == 0) {
ret = blkio_io_uring_open(bs, options, flags, errp);
} else if (strcmp(blkio_driver, DRIVER_NVME_IO_URING) == 0) {
} else if (strcmp(blkio_driver, "nvme-io_uring") == 0) {
ret = blkio_nvme_io_uring(bs, options, flags, errp);
} else if (strcmp(blkio_driver, DRIVER_VIRTIO_BLK_VFIO_PCI) == 0) {
} else if (strcmp(blkio_driver, "virtio-blk-vfio-pci") == 0) {
ret = blkio_virtio_blk_common_open(bs, options, flags, errp);
} else if (strcmp(blkio_driver, DRIVER_VIRTIO_BLK_VHOST_USER) == 0) {
} else if (strcmp(blkio_driver, "virtio-blk-vhost-user") == 0) {
ret = blkio_virtio_blk_common_open(bs, options, flags, errp);
} else if (strcmp(blkio_driver, DRIVER_VIRTIO_BLK_VHOST_VDPA) == 0) {
} else if (strcmp(blkio_driver, "virtio-blk-vhost-vdpa") == 0) {
ret = blkio_virtio_blk_common_open(bs, options, flags, errp);
} else {
g_assert_not_reached();
Expand Down Expand Up @@ -1028,49 +1018,63 @@ static void blkio_refresh_limits(BlockDriverState *bs, Error **errp)
* - truncate
*/

#define BLKIO_DRIVER(name, ...) \
{ \
.format_name = name, \
.protocol_name = name, \
.instance_size = sizeof(BDRVBlkioState), \
.bdrv_file_open = blkio_file_open, \
.bdrv_close = blkio_close, \
.bdrv_co_getlength = blkio_co_getlength, \
.bdrv_co_truncate = blkio_truncate, \
.bdrv_co_get_info = blkio_co_get_info, \
.bdrv_attach_aio_context = blkio_attach_aio_context, \
.bdrv_detach_aio_context = blkio_detach_aio_context, \
.bdrv_co_pdiscard = blkio_co_pdiscard, \
.bdrv_co_preadv = blkio_co_preadv, \
.bdrv_co_pwritev = blkio_co_pwritev, \
.bdrv_co_flush_to_disk = blkio_co_flush, \
.bdrv_co_pwrite_zeroes = blkio_co_pwrite_zeroes, \
.bdrv_refresh_limits = blkio_refresh_limits, \
.bdrv_register_buf = blkio_register_buf, \
.bdrv_unregister_buf = blkio_unregister_buf, \
__VA_ARGS__ \
}

static BlockDriver bdrv_io_uring = BLKIO_DRIVER(
DRIVER_IO_URING,
.bdrv_needs_filename = true,
);

static BlockDriver bdrv_nvme_io_uring = BLKIO_DRIVER(
DRIVER_NVME_IO_URING,
);

static BlockDriver bdrv_virtio_blk_vfio_pci = BLKIO_DRIVER(
DRIVER_VIRTIO_BLK_VFIO_PCI
);
/*
* Do not include .format_name and .protocol_name because module_block.py
* does not parse macros in the source code.
*/
#define BLKIO_DRIVER_COMMON \
.instance_size = sizeof(BDRVBlkioState), \
.bdrv_file_open = blkio_file_open, \
.bdrv_close = blkio_close, \
.bdrv_co_getlength = blkio_co_getlength, \
.bdrv_co_truncate = blkio_truncate, \
.bdrv_co_get_info = blkio_co_get_info, \
.bdrv_attach_aio_context = blkio_attach_aio_context, \
.bdrv_detach_aio_context = blkio_detach_aio_context, \
.bdrv_co_pdiscard = blkio_co_pdiscard, \
.bdrv_co_preadv = blkio_co_preadv, \
.bdrv_co_pwritev = blkio_co_pwritev, \
.bdrv_co_flush_to_disk = blkio_co_flush, \
.bdrv_co_pwrite_zeroes = blkio_co_pwrite_zeroes, \
.bdrv_refresh_limits = blkio_refresh_limits, \
.bdrv_register_buf = blkio_register_buf, \
.bdrv_unregister_buf = blkio_unregister_buf,

static BlockDriver bdrv_virtio_blk_vhost_user = BLKIO_DRIVER(
DRIVER_VIRTIO_BLK_VHOST_USER
);
/*
* Use the same .format_name and .protocol_name as the libblkio driver name for
* consistency.
*/

static BlockDriver bdrv_virtio_blk_vhost_vdpa = BLKIO_DRIVER(
DRIVER_VIRTIO_BLK_VHOST_VDPA
);
static BlockDriver bdrv_io_uring = {
.format_name = "io_uring",
.protocol_name = "io_uring",
.bdrv_needs_filename = true,
BLKIO_DRIVER_COMMON
};

static BlockDriver bdrv_nvme_io_uring = {
.format_name = "nvme-io_uring",
.protocol_name = "nvme-io_uring",
BLKIO_DRIVER_COMMON
};

static BlockDriver bdrv_virtio_blk_vfio_pci = {
.format_name = "virtio-blk-vfio-pci",
.protocol_name = "virtio-blk-vfio-pci",
BLKIO_DRIVER_COMMON
};

static BlockDriver bdrv_virtio_blk_vhost_user = {
.format_name = "virtio-blk-vhost-user",
.protocol_name = "virtio-blk-vhost-user",
BLKIO_DRIVER_COMMON
};

static BlockDriver bdrv_virtio_blk_vhost_vdpa = {
.format_name = "virtio-blk-vhost-vdpa",
.protocol_name = "virtio-blk-vhost-vdpa",
BLKIO_DRIVER_COMMON
};

static void bdrv_blkio_init(void)
{
Expand Down

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