block/blklogwrites.c - third_party/qemu - Git at Google

 /*
  * Write logging blk driver based on blkverify and blkdebug.
  *
  * Copyright (c) 2017 Tuomas Tynkkynen <tuomas@tuxera.com>
  * Copyright (c) 2018 Aapo Vienamo <aapo@tuxera.com>
  * Copyright (c) 2018 Ari Sundholm <ari@tuxera.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
  */

 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "qemu/sockets.h" /* for EINPROGRESS on Windows */
 #include "block/block_int.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qstring.h"
 #include "qemu/cutils.h"
 #include "qemu/module.h"
 #include "qemu/option.h"

 /* Disk format stuff - taken from Linux drivers/md/dm-log-writes.c */

 #define LOG_FLUSH_FLAG   (1 << 0)
 #define LOG_FUA_FLAG     (1 << 1)
 #define LOG_DISCARD_FLAG (1 << 2)
 #define LOG_MARK_FLAG    (1 << 3)
 #define LOG_FLAG_MASK    (LOG_FLUSH_FLAG \
                          | LOG_FUA_FLAG \
                          | LOG_DISCARD_FLAG \
                          | LOG_MARK_FLAG)

 #define WRITE_LOG_VERSION 1ULL
 #define WRITE_LOG_MAGIC 0x6a736677736872ULL

 /* All fields are little-endian. */
 struct log_write_super {
     uint64_t magic;
     uint64_t version;
     uint64_t nr_entries;
     uint32_t sectorsize;
 } QEMU_PACKED;

 struct log_write_entry {
     uint64_t sector;
     uint64_t nr_sectors;
     uint64_t flags;
     uint64_t data_len;
 } QEMU_PACKED;

 /* End of disk format structures. */

 typedef struct {
     BdrvChild *log_file;
     uint32_t sectorsize;
     uint32_t sectorbits;
     uint64_t cur_log_sector;
     uint64_t nr_entries;
     uint64_t update_interval;
 } BDRVBlkLogWritesState;

 static QemuOptsList runtime_opts = {
     .name = "blklogwrites",
     .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
     .desc = {
         {
             .name = "log-append",
             .type = QEMU_OPT_BOOL,
             .help = "Append to an existing log",
         },
         {
             .name = "log-sector-size",
             .type = QEMU_OPT_SIZE,
             .help = "Log sector size",
         },
         {
             .name = "log-super-update-interval",
             .type = QEMU_OPT_NUMBER,
             .help = "Log superblock update interval (# of write requests)",
         },
         { /* end of list */ }
     },
 };

 static inline uint32_t blk_log_writes_log2(uint32_t value)
 {
     assert(value > 0);
     return 31 - clz32(value);
 }

 static inline bool blk_log_writes_sector_size_valid(uint32_t sector_size)
 {
     return is_power_of_2(sector_size) &&
         sector_size >= sizeof(struct log_write_super) &&
         sector_size >= sizeof(struct log_write_entry) &&
         sector_size < (1ull << 24);
 }

 static uint64_t blk_log_writes_find_cur_log_sector(BdrvChild *log,
                                                    uint32_t sector_size,
                                                    uint64_t nr_entries,
                                                    Error **errp)
 {
     uint64_t cur_sector = 1;
     uint64_t cur_idx = 0;
     uint32_t sector_bits = blk_log_writes_log2(sector_size);
     struct log_write_entry cur_entry;

     while (cur_idx < nr_entries) {
         int read_ret = bdrv_pread(log, cur_sector << sector_bits, &cur_entry,
                                   sizeof(cur_entry));
         if (read_ret < 0) {
             error_setg_errno(errp, -read_ret,
                              "Failed to read log entry %"PRIu64, cur_idx);
             return (uint64_t)-1ull;
         }

         if (cur_entry.flags & ~cpu_to_le64(LOG_FLAG_MASK)) {
             error_setg(errp, "Invalid flags 0x%"PRIx64" in log entry %"PRIu64,
                        le64_to_cpu(cur_entry.flags), cur_idx);
             return (uint64_t)-1ull;
         }

         /* Account for the sector of the entry itself */
         ++cur_sector;

         /*
          * Account for the data of the write.
          * For discards, this data is not present.
          */
         if (!(cur_entry.flags & cpu_to_le64(LOG_DISCARD_FLAG))) {
             cur_sector += le64_to_cpu(cur_entry.nr_sectors);
         }

         ++cur_idx;
     }

     return cur_sector;
 }

 static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
                                Error **errp)
 {
     BDRVBlkLogWritesState *s = bs->opaque;
     QemuOpts *opts;
     Error *local_err = NULL;
     int ret;
     uint64_t log_sector_size;
     bool log_append;

     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
     qemu_opts_absorb_qdict(opts, options, &local_err);
     if (local_err) {
         ret = -EINVAL;
         error_propagate(errp, local_err);
         goto fail;
     }

     /* Open the file */
     bs->file = bdrv_open_child(NULL, options, "file", bs, &child_file, false,
                                &local_err);
     if (local_err) {
         ret = -EINVAL;
         error_propagate(errp, local_err);
         goto fail;
     }

     /* Open the log file */
     s->log_file = bdrv_open_child(NULL, options, "log", bs, &child_file, false,
                                   &local_err);
     if (local_err) {
         ret = -EINVAL;
         error_propagate(errp, local_err);
         goto fail;
     }

     log_append = qemu_opt_get_bool(opts, "log-append", false);

     if (log_append) {
         struct log_write_super log_sb = { 0, 0, 0, 0 };

         if (qemu_opt_find(opts, "log-sector-size")) {
             ret = -EINVAL;
             error_setg(errp, "log-append and log-sector-size are mutually "
                        "exclusive");
             goto fail_log;
         }

         /* Read log superblock or fake one for an empty log */
         if (!bdrv_getlength(s->log_file->bs)) {
             log_sb.magic      = cpu_to_le64(WRITE_LOG_MAGIC);
             log_sb.version    = cpu_to_le64(WRITE_LOG_VERSION);
             log_sb.nr_entries = cpu_to_le64(0);
             log_sb.sectorsize = cpu_to_le32(BDRV_SECTOR_SIZE);
         } else {
             ret = bdrv_pread(s->log_file, 0, &log_sb, sizeof(log_sb));
             if (ret < 0) {
                 error_setg_errno(errp, -ret, "Could not read log superblock");
                 goto fail_log;
             }
         }

         if (log_sb.magic != cpu_to_le64(WRITE_LOG_MAGIC)) {
             ret = -EINVAL;
             error_setg(errp, "Invalid log superblock magic");
             goto fail_log;
         }

         if (log_sb.version != cpu_to_le64(WRITE_LOG_VERSION)) {
             ret = -EINVAL;
             error_setg(errp, "Unsupported log version %"PRIu64,
                        le64_to_cpu(log_sb.version));
             goto fail_log;
         }

         log_sector_size = le32_to_cpu(log_sb.sectorsize);
         s->cur_log_sector = 1;
         s->nr_entries = 0;

         if (blk_log_writes_sector_size_valid(log_sector_size)) {
             s->cur_log_sector =
                 blk_log_writes_find_cur_log_sector(s->log_file, log_sector_size,
                                     le64_to_cpu(log_sb.nr_entries), &local_err);
             if (local_err) {
                 ret = -EINVAL;
                 error_propagate(errp, local_err);
                 goto fail_log;
             }

             s->nr_entries = le64_to_cpu(log_sb.nr_entries);
         }
     } else {
         log_sector_size = qemu_opt_get_size(opts, "log-sector-size",
                                             BDRV_SECTOR_SIZE);
         s->cur_log_sector = 1;
         s->nr_entries = 0;
     }

     if (!blk_log_writes_sector_size_valid(log_sector_size)) {
         ret = -EINVAL;
         error_setg(errp, "Invalid log sector size %"PRIu64, log_sector_size);
         goto fail_log;
     }

     s->sectorsize = log_sector_size;
     s->sectorbits = blk_log_writes_log2(log_sector_size);
     s->update_interval = qemu_opt_get_number(opts, "log-super-update-interval",
                                              4096);
     if (!s->update_interval) {
         ret = -EINVAL;
         error_setg(errp, "Invalid log superblock update interval %"PRIu64,
                    s->update_interval);
         goto fail_log;
     }

     ret = 0;
 fail_log:
     if (ret < 0) {
         bdrv_unref_child(bs, s->log_file);
         s->log_file = NULL;
     }
 fail:
     if (ret < 0) {
         bdrv_unref_child(bs, bs->file);
         bs->file = NULL;
     }
     qemu_opts_del(opts);
     return ret;
 }

 static void blk_log_writes_close(BlockDriverState *bs)
 {
     BDRVBlkLogWritesState *s = bs->opaque;

     bdrv_unref_child(bs, s->log_file);
     s->log_file = NULL;
 }

 static int64_t blk_log_writes_getlength(BlockDriverState *bs)
 {
     return bdrv_getlength(bs->file->bs);
 }

 static void blk_log_writes_child_perm(BlockDriverState *bs, BdrvChild *c,
                                       const BdrvChildRole *role,
                                       BlockReopenQueue *ro_q,
                                       uint64_t perm, uint64_t shrd,
                                       uint64_t *nperm, uint64_t *nshrd)
 {
     if (!c) {
         *nperm = perm & DEFAULT_PERM_PASSTHROUGH;
         *nshrd = (shrd & DEFAULT_PERM_PASSTHROUGH) | DEFAULT_PERM_UNCHANGED;
         return;
     }

     if (!strcmp(c->name, "log")) {
         bdrv_format_default_perms(bs, c, role, ro_q, perm, shrd, nperm, nshrd);
     } else {
         bdrv_filter_default_perms(bs, c, role, ro_q, perm, shrd, nperm, nshrd);
     }
 }

 static void blk_log_writes_refresh_limits(BlockDriverState *bs, Error **errp)
 {
     BDRVBlkLogWritesState *s = bs->opaque;
     bs->bl.request_alignment = s->sectorsize;
 }

 static int coroutine_fn
 blk_log_writes_co_preadv(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
                          QEMUIOVector *qiov, int flags)
 {
     return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
 }

 typedef struct BlkLogWritesFileReq {
     BlockDriverState *bs;
     uint64_t offset;
     uint64_t bytes;
     int file_flags;
     QEMUIOVector *qiov;
     int (*func)(struct BlkLogWritesFileReq *r);
     int file_ret;
 } BlkLogWritesFileReq;

 typedef struct {
     BlockDriverState *bs;
     QEMUIOVector *qiov;
     struct log_write_entry entry;
     uint64_t zero_size;
     int log_ret;
 } BlkLogWritesLogReq;

 static void coroutine_fn blk_log_writes_co_do_log(BlkLogWritesLogReq *lr)
 {
     BDRVBlkLogWritesState *s = lr->bs->opaque;
     uint64_t cur_log_offset = s->cur_log_sector << s->sectorbits;

     s->nr_entries++;
     s->cur_log_sector +=
             ROUND_UP(lr->qiov->size, s->sectorsize) >> s->sectorbits;

     lr->log_ret = bdrv_co_pwritev(s->log_file, cur_log_offset, lr->qiov->size,
                                   lr->qiov, 0);

     /* Logging for the "write zeroes" operation */
     if (lr->log_ret == 0 && lr->zero_size) {
         cur_log_offset = s->cur_log_sector << s->sectorbits;
         s->cur_log_sector +=
                 ROUND_UP(lr->zero_size, s->sectorsize) >> s->sectorbits;

         lr->log_ret = bdrv_co_pwrite_zeroes(s->log_file, cur_log_offset,
                                             lr->zero_size, 0);
     }

     /* Update super block on flush or every update interval */
     if (lr->log_ret == 0 && ((lr->entry.flags & LOG_FLUSH_FLAG)
         || (s->nr_entries % s->update_interval == 0)))
     {
         struct log_write_super super = {
             .magic      = cpu_to_le64(WRITE_LOG_MAGIC),
             .version    = cpu_to_le64(WRITE_LOG_VERSION),
             .nr_entries = cpu_to_le64(s->nr_entries),
             .sectorsize = cpu_to_le32(s->sectorsize),
         };
         void *zeroes = g_malloc0(s->sectorsize - sizeof(super));
         QEMUIOVector qiov;

         qemu_iovec_init(&qiov, 2);
         qemu_iovec_add(&qiov, &super, sizeof(super));
         qemu_iovec_add(&qiov, zeroes, s->sectorsize - sizeof(super));

         lr->log_ret =
             bdrv_co_pwritev(s->log_file, 0, s->sectorsize, &qiov, 0);
         if (lr->log_ret == 0) {
             lr->log_ret = bdrv_co_flush(s->log_file->bs);
         }
         qemu_iovec_destroy(&qiov);
         g_free(zeroes);
     }
 }

 static void coroutine_fn blk_log_writes_co_do_file(BlkLogWritesFileReq *fr)
 {
     fr->file_ret = fr->func(fr);
 }

 static int coroutine_fn
 blk_log_writes_co_log(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
                       QEMUIOVector *qiov, int flags,
                       int (*file_func)(BlkLogWritesFileReq *r),
                       uint64_t entry_flags, bool is_zero_write)
 {
     QEMUIOVector log_qiov;
     size_t niov = qiov ? qiov->niov : 0;
     BDRVBlkLogWritesState *s = bs->opaque;
     BlkLogWritesFileReq fr = {
         .bs         = bs,
         .offset     = offset,
         .bytes      = bytes,
         .file_flags = flags,
         .qiov       = qiov,
         .func       = file_func,
     };
     BlkLogWritesLogReq lr = {
         .bs             = bs,
         .qiov           = &log_qiov,
         .entry = {
             .sector     = cpu_to_le64(offset >> s->sectorbits),
             .nr_sectors = cpu_to_le64(bytes >> s->sectorbits),
             .flags      = cpu_to_le64(entry_flags),
             .data_len   = 0,
         },
         .zero_size = is_zero_write ? bytes : 0,
     };
     void *zeroes = g_malloc0(s->sectorsize - sizeof(lr.entry));

     assert((1 << s->sectorbits) == s->sectorsize);
     assert(bs->bl.request_alignment == s->sectorsize);
     assert(QEMU_IS_ALIGNED(offset, bs->bl.request_alignment));
     assert(QEMU_IS_ALIGNED(bytes, bs->bl.request_alignment));

     qemu_iovec_init(&log_qiov, niov + 2);
     qemu_iovec_add(&log_qiov, &lr.entry, sizeof(lr.entry));
     qemu_iovec_add(&log_qiov, zeroes, s->sectorsize - sizeof(lr.entry));
     if (qiov) {
         qemu_iovec_concat(&log_qiov, qiov, 0, qiov->size);
     }

     blk_log_writes_co_do_file(&fr);
     blk_log_writes_co_do_log(&lr);

     qemu_iovec_destroy(&log_qiov);
     g_free(zeroes);

     if (lr.log_ret < 0) {
         return lr.log_ret;
     }

     return fr.file_ret;
 }

 static int coroutine_fn
 blk_log_writes_co_do_file_pwritev(BlkLogWritesFileReq *fr)
 {
     return bdrv_co_pwritev(fr->bs->file, fr->offset, fr->bytes,
                            fr->qiov, fr->file_flags);
 }

 static int coroutine_fn
 blk_log_writes_co_do_file_pwrite_zeroes(BlkLogWritesFileReq *fr)
 {
     return bdrv_co_pwrite_zeroes(fr->bs->file, fr->offset, fr->bytes,
                                  fr->file_flags);
 }

 static int coroutine_fn blk_log_writes_co_do_file_flush(BlkLogWritesFileReq *fr)
 {
     return bdrv_co_flush(fr->bs->file->bs);
 }

 static int coroutine_fn
 blk_log_writes_co_do_file_pdiscard(BlkLogWritesFileReq *fr)
 {
     return bdrv_co_pdiscard(fr->bs->file, fr->offset, fr->bytes);
 }

 static int coroutine_fn
 blk_log_writes_co_pwritev(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
                           QEMUIOVector *qiov, int flags)
 {
     return blk_log_writes_co_log(bs, offset, bytes, qiov, flags,
                                  blk_log_writes_co_do_file_pwritev, 0, false);
 }

 static int coroutine_fn
 blk_log_writes_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int bytes,
                                 BdrvRequestFlags flags)
 {
     return blk_log_writes_co_log(bs, offset, bytes, NULL, flags,
                                  blk_log_writes_co_do_file_pwrite_zeroes, 0,
                                  true);
 }

 static int coroutine_fn blk_log_writes_co_flush_to_disk(BlockDriverState *bs)
 {
     return blk_log_writes_co_log(bs, 0, 0, NULL, 0,
                                  blk_log_writes_co_do_file_flush,
                                  LOG_FLUSH_FLAG, false);
 }

 static int coroutine_fn
 blk_log_writes_co_pdiscard(BlockDriverState *bs, int64_t offset, int count)
 {
     return blk_log_writes_co_log(bs, offset, count, NULL, 0,
                                  blk_log_writes_co_do_file_pdiscard,
                                  LOG_DISCARD_FLAG, false);
 }

 static const char *const blk_log_writes_strong_runtime_opts[] = {
     "log-append",
     "log-sector-size",

     NULL
 };

 static BlockDriver bdrv_blk_log_writes = {
     .format_name            = "blklogwrites",
     .instance_size          = sizeof(BDRVBlkLogWritesState),

     .bdrv_open              = blk_log_writes_open,
     .bdrv_close             = blk_log_writes_close,
     .bdrv_getlength         = blk_log_writes_getlength,
     .bdrv_child_perm        = blk_log_writes_child_perm,
     .bdrv_refresh_limits    = blk_log_writes_refresh_limits,

     .bdrv_co_preadv         = blk_log_writes_co_preadv,
     .bdrv_co_pwritev        = blk_log_writes_co_pwritev,
     .bdrv_co_pwrite_zeroes  = blk_log_writes_co_pwrite_zeroes,
     .bdrv_co_flush_to_disk  = blk_log_writes_co_flush_to_disk,
     .bdrv_co_pdiscard       = blk_log_writes_co_pdiscard,
     .bdrv_co_block_status   = bdrv_co_block_status_from_file,

     .is_filter              = true,
     .strong_runtime_opts    = blk_log_writes_strong_runtime_opts,
 };

 static void bdrv_blk_log_writes_init(void)
 {
     bdrv_register(&bdrv_blk_log_writes);
 }

 block_init(bdrv_blk_log_writes_init);
	/*
	* Write logging blk driver based on blkverify and blkdebug.
	*
	* Copyright (c) 2017 Tuomas Tynkkynen <tuomas@tuxera.com>
	* Copyright (c) 2018 Aapo Vienamo <aapo@tuxera.com>
	* Copyright (c) 2018 Ari Sundholm <ari@tuxera.com>
	*
	* This work is licensed under the terms of the GNU GPL, version 2 or later.
	* See the COPYING file in the top-level directory.
	*/

	#include "qemu/osdep.h"
	#include "qapi/error.h"
	#include "qemu/sockets.h" /* for EINPROGRESS on Windows */
	#include "block/block_int.h"
	#include "qapi/qmp/qdict.h"
	#include "qapi/qmp/qstring.h"
	#include "qemu/cutils.h"
	#include "qemu/module.h"
	#include "qemu/option.h"

	/* Disk format stuff - taken from Linux drivers/md/dm-log-writes.c */

	#define LOG_FLUSH_FLAG (1 << 0)
	#define LOG_FUA_FLAG (1 << 1)
	#define LOG_DISCARD_FLAG (1 << 2)
	#define LOG_MARK_FLAG (1 << 3)
	#define LOG_FLAG_MASK (LOG_FLUSH_FLAG \
	\| LOG_FUA_FLAG \
	\| LOG_DISCARD_FLAG \
	\| LOG_MARK_FLAG)

	#define WRITE_LOG_VERSION 1ULL
	#define WRITE_LOG_MAGIC 0x6a736677736872ULL

	/* All fields are little-endian. */
	struct log_write_super {
	uint64_t magic;
	uint64_t version;
	uint64_t nr_entries;
	uint32_t sectorsize;
	} QEMU_PACKED;

	struct log_write_entry {
	uint64_t sector;
	uint64_t nr_sectors;
	uint64_t flags;
	uint64_t data_len;
	} QEMU_PACKED;

	/* End of disk format structures. */

	typedef struct {
	BdrvChild *log_file;
	uint32_t sectorsize;
	uint32_t sectorbits;
	uint64_t cur_log_sector;
	uint64_t nr_entries;
	uint64_t update_interval;
	} BDRVBlkLogWritesState;

	static QemuOptsList runtime_opts = {
	.name = "blklogwrites",
	.head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
	.desc = {
	{
	.name = "log-append",
	.type = QEMU_OPT_BOOL,
	.help = "Append to an existing log",
	},
	{
	.name = "log-sector-size",
	.type = QEMU_OPT_SIZE,
	.help = "Log sector size",
	},
	{
	.name = "log-super-update-interval",
	.type = QEMU_OPT_NUMBER,
	.help = "Log superblock update interval (# of write requests)",
	},
	{ /* end of list */ }
	},
	};

	static inline uint32_t blk_log_writes_log2(uint32_t value)
	{
	assert(value > 0);
	return 31 - clz32(value);
	}

	static inline bool blk_log_writes_sector_size_valid(uint32_t sector_size)
	{
	return is_power_of_2(sector_size) &&
	sector_size >= sizeof(struct log_write_super) &&
	sector_size >= sizeof(struct log_write_entry) &&
	sector_size < (1ull << 24);
	}

	static uint64_t blk_log_writes_find_cur_log_sector(BdrvChild *log,
	uint32_t sector_size,
	uint64_t nr_entries,
	Error **errp)
	{
	uint64_t cur_sector = 1;
	uint64_t cur_idx = 0;
	uint32_t sector_bits = blk_log_writes_log2(sector_size);
	struct log_write_entry cur_entry;

	while (cur_idx < nr_entries) {
	int read_ret = bdrv_pread(log, cur_sector << sector_bits, &cur_entry,
	sizeof(cur_entry));
	if (read_ret < 0) {
	error_setg_errno(errp, -read_ret,
	"Failed to read log entry %"PRIu64, cur_idx);
	return (uint64_t)-1ull;
	}

	if (cur_entry.flags & ~cpu_to_le64(LOG_FLAG_MASK)) {
	error_setg(errp, "Invalid flags 0x%"PRIx64" in log entry %"PRIu64,
	le64_to_cpu(cur_entry.flags), cur_idx);
	return (uint64_t)-1ull;
	}

	/* Account for the sector of the entry itself */
	++cur_sector;

	/*
	* Account for the data of the write.
	* For discards, this data is not present.
	*/
	if (!(cur_entry.flags & cpu_to_le64(LOG_DISCARD_FLAG))) {
	cur_sector += le64_to_cpu(cur_entry.nr_sectors);
	}

	++cur_idx;
	}

	return cur_sector;
	}

	static int blk_log_writes_open(BlockDriverState bs, QDict options, int flags,
	Error **errp)
	{
	BDRVBlkLogWritesState *s = bs->opaque;
	QemuOpts *opts;
	Error *local_err = NULL;
	int ret;
	uint64_t log_sector_size;
	bool log_append;

	opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
	qemu_opts_absorb_qdict(opts, options, &local_err);
	if (local_err) {
	ret = -EINVAL;
	error_propagate(errp, local_err);
	goto fail;
	}

	/* Open the file */
	bs->file = bdrv_open_child(NULL, options, "file", bs, &child_file, false,
	&local_err);
	if (local_err) {
	ret = -EINVAL;
	error_propagate(errp, local_err);
	goto fail;
	}

	/* Open the log file */
	s->log_file = bdrv_open_child(NULL, options, "log", bs, &child_file, false,
	&local_err);
	if (local_err) {
	ret = -EINVAL;
	error_propagate(errp, local_err);
	goto fail;
	}

	log_append = qemu_opt_get_bool(opts, "log-append", false);

	if (log_append) {
	struct log_write_super log_sb = { 0, 0, 0, 0 };

	if (qemu_opt_find(opts, "log-sector-size")) {
	ret = -EINVAL;
	error_setg(errp, "log-append and log-sector-size are mutually "
	"exclusive");
	goto fail_log;
	}

	/* Read log superblock or fake one for an empty log */
	if (!bdrv_getlength(s->log_file->bs)) {
	log_sb.magic = cpu_to_le64(WRITE_LOG_MAGIC);
	log_sb.version = cpu_to_le64(WRITE_LOG_VERSION);
	log_sb.nr_entries = cpu_to_le64(0);
	log_sb.sectorsize = cpu_to_le32(BDRV_SECTOR_SIZE);
	} else {
	ret = bdrv_pread(s->log_file, 0, &log_sb, sizeof(log_sb));
	if (ret < 0) {
	error_setg_errno(errp, -ret, "Could not read log superblock");
	goto fail_log;
	}
	}

	if (log_sb.magic != cpu_to_le64(WRITE_LOG_MAGIC)) {
	ret = -EINVAL;
	error_setg(errp, "Invalid log superblock magic");
	goto fail_log;
	}

	if (log_sb.version != cpu_to_le64(WRITE_LOG_VERSION)) {
	ret = -EINVAL;
	error_setg(errp, "Unsupported log version %"PRIu64,
	le64_to_cpu(log_sb.version));
	goto fail_log;
	}

	log_sector_size = le32_to_cpu(log_sb.sectorsize);
	s->cur_log_sector = 1;
	s->nr_entries = 0;

	if (blk_log_writes_sector_size_valid(log_sector_size)) {
	s->cur_log_sector =
	blk_log_writes_find_cur_log_sector(s->log_file, log_sector_size,
	le64_to_cpu(log_sb.nr_entries), &local_err);
	if (local_err) {
	ret = -EINVAL;
	error_propagate(errp, local_err);
	goto fail_log;
	}

	s->nr_entries = le64_to_cpu(log_sb.nr_entries);
	}
	} else {
	log_sector_size = qemu_opt_get_size(opts, "log-sector-size",
	BDRV_SECTOR_SIZE);
	s->cur_log_sector = 1;
	s->nr_entries = 0;
	}

	if (!blk_log_writes_sector_size_valid(log_sector_size)) {
	ret = -EINVAL;
	error_setg(errp, "Invalid log sector size %"PRIu64, log_sector_size);
	goto fail_log;
	}

	s->sectorsize = log_sector_size;
	s->sectorbits = blk_log_writes_log2(log_sector_size);
	s->update_interval = qemu_opt_get_number(opts, "log-super-update-interval",
	4096);
	if (!s->update_interval) {
	ret = -EINVAL;
	error_setg(errp, "Invalid log superblock update interval %"PRIu64,
	s->update_interval);
	goto fail_log;
	}

	ret = 0;
	fail_log:
	if (ret < 0) {
	bdrv_unref_child(bs, s->log_file);
	s->log_file = NULL;
	}
	fail:
	if (ret < 0) {
	bdrv_unref_child(bs, bs->file);
	bs->file = NULL;
	}
	qemu_opts_del(opts);
	return ret;
	}

	static void blk_log_writes_close(BlockDriverState *bs)
	{
	BDRVBlkLogWritesState *s = bs->opaque;

	bdrv_unref_child(bs, s->log_file);
	s->log_file = NULL;
	}

	static int64_t blk_log_writes_getlength(BlockDriverState *bs)
	{
	return bdrv_getlength(bs->file->bs);
	}

	static void blk_log_writes_child_perm(BlockDriverState bs, BdrvChild c,
	const BdrvChildRole *role,
	BlockReopenQueue *ro_q,
	uint64_t perm, uint64_t shrd,
	uint64_t nperm, uint64_t nshrd)
	{
	if (!c) {
	*nperm = perm & DEFAULT_PERM_PASSTHROUGH;
	*nshrd = (shrd & DEFAULT_PERM_PASSTHROUGH) \| DEFAULT_PERM_UNCHANGED;
	return;
	}

	if (!strcmp(c->name, "log")) {
	bdrv_format_default_perms(bs, c, role, ro_q, perm, shrd, nperm, nshrd);
	} else {
	bdrv_filter_default_perms(bs, c, role, ro_q, perm, shrd, nperm, nshrd);
	}
	}

	static void blk_log_writes_refresh_limits(BlockDriverState bs, Error *errp)
	{
	BDRVBlkLogWritesState *s = bs->opaque;
	bs->bl.request_alignment = s->sectorsize;
	}

	static int coroutine_fn
	blk_log_writes_co_preadv(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
	QEMUIOVector *qiov, int flags)
	{
	return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
	}

	typedef struct BlkLogWritesFileReq {
	BlockDriverState *bs;
	uint64_t offset;
	uint64_t bytes;
	int file_flags;
	QEMUIOVector *qiov;
	int (func)(struct BlkLogWritesFileReq r);
	int file_ret;
	} BlkLogWritesFileReq;

	typedef struct {
	BlockDriverState *bs;
	QEMUIOVector *qiov;
	struct log_write_entry entry;
	uint64_t zero_size;
	int log_ret;
	} BlkLogWritesLogReq;

	static void coroutine_fn blk_log_writes_co_do_log(BlkLogWritesLogReq *lr)
	{
	BDRVBlkLogWritesState *s = lr->bs->opaque;
	uint64_t cur_log_offset = s->cur_log_sector << s->sectorbits;

	s->nr_entries++;
	s->cur_log_sector +=
	ROUND_UP(lr->qiov->size, s->sectorsize) >> s->sectorbits;

	lr->log_ret = bdrv_co_pwritev(s->log_file, cur_log_offset, lr->qiov->size,
	lr->qiov, 0);

	/* Logging for the "write zeroes" operation */
	if (lr->log_ret == 0 && lr->zero_size) {
	cur_log_offset = s->cur_log_sector << s->sectorbits;
	s->cur_log_sector +=
	ROUND_UP(lr->zero_size, s->sectorsize) >> s->sectorbits;

	lr->log_ret = bdrv_co_pwrite_zeroes(s->log_file, cur_log_offset,
	lr->zero_size, 0);
	}

	/* Update super block on flush or every update interval */
	if (lr->log_ret == 0 && ((lr->entry.flags & LOG_FLUSH_FLAG)
	\|\| (s->nr_entries % s->update_interval == 0)))
	{
	struct log_write_super super = {
	.magic = cpu_to_le64(WRITE_LOG_MAGIC),
	.version = cpu_to_le64(WRITE_LOG_VERSION),
	.nr_entries = cpu_to_le64(s->nr_entries),
	.sectorsize = cpu_to_le32(s->sectorsize),
	};
	void *zeroes = g_malloc0(s->sectorsize - sizeof(super));
	QEMUIOVector qiov;

	qemu_iovec_init(&qiov, 2);
	qemu_iovec_add(&qiov, &super, sizeof(super));
	qemu_iovec_add(&qiov, zeroes, s->sectorsize - sizeof(super));

	lr->log_ret =
	bdrv_co_pwritev(s->log_file, 0, s->sectorsize, &qiov, 0);
	if (lr->log_ret == 0) {
	lr->log_ret = bdrv_co_flush(s->log_file->bs);
	}
	qemu_iovec_destroy(&qiov);
	g_free(zeroes);
	}
	}

	static void coroutine_fn blk_log_writes_co_do_file(BlkLogWritesFileReq *fr)
	{
	fr->file_ret = fr->func(fr);
	}

	static int coroutine_fn
	blk_log_writes_co_log(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
	QEMUIOVector *qiov, int flags,
	int (file_func)(BlkLogWritesFileReq r),
	uint64_t entry_flags, bool is_zero_write)
	{
	QEMUIOVector log_qiov;
	size_t niov = qiov ? qiov->niov : 0;
	BDRVBlkLogWritesState *s = bs->opaque;
	BlkLogWritesFileReq fr = {
	.bs = bs,
	.offset = offset,
	.bytes = bytes,
	.file_flags = flags,
	.qiov = qiov,
	.func = file_func,
	};
	BlkLogWritesLogReq lr = {
	.bs = bs,
	.qiov = &log_qiov,
	.entry = {
	.sector = cpu_to_le64(offset >> s->sectorbits),
	.nr_sectors = cpu_to_le64(bytes >> s->sectorbits),
	.flags = cpu_to_le64(entry_flags),
	.data_len = 0,
	},
	.zero_size = is_zero_write ? bytes : 0,
	};
	void *zeroes = g_malloc0(s->sectorsize - sizeof(lr.entry));

	assert((1 << s->sectorbits) == s->sectorsize);
	assert(bs->bl.request_alignment == s->sectorsize);
	assert(QEMU_IS_ALIGNED(offset, bs->bl.request_alignment));
	assert(QEMU_IS_ALIGNED(bytes, bs->bl.request_alignment));

	qemu_iovec_init(&log_qiov, niov + 2);
	qemu_iovec_add(&log_qiov, &lr.entry, sizeof(lr.entry));
	qemu_iovec_add(&log_qiov, zeroes, s->sectorsize - sizeof(lr.entry));
	if (qiov) {
	qemu_iovec_concat(&log_qiov, qiov, 0, qiov->size);
	}

	blk_log_writes_co_do_file(&fr);
	blk_log_writes_co_do_log(&lr);

	qemu_iovec_destroy(&log_qiov);
	g_free(zeroes);

	if (lr.log_ret < 0) {
	return lr.log_ret;
	}

	return fr.file_ret;
	}

	static int coroutine_fn
	blk_log_writes_co_do_file_pwritev(BlkLogWritesFileReq *fr)
	{
	return bdrv_co_pwritev(fr->bs->file, fr->offset, fr->bytes,
	fr->qiov, fr->file_flags);
	}

	static int coroutine_fn
	blk_log_writes_co_do_file_pwrite_zeroes(BlkLogWritesFileReq *fr)
	{
	return bdrv_co_pwrite_zeroes(fr->bs->file, fr->offset, fr->bytes,
	fr->file_flags);
	}

	static int coroutine_fn blk_log_writes_co_do_file_flush(BlkLogWritesFileReq *fr)
	{
	return bdrv_co_flush(fr->bs->file->bs);
	}

	static int coroutine_fn
	blk_log_writes_co_do_file_pdiscard(BlkLogWritesFileReq *fr)
	{
	return bdrv_co_pdiscard(fr->bs->file, fr->offset, fr->bytes);
	}

	static int coroutine_fn
	blk_log_writes_co_pwritev(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
	QEMUIOVector *qiov, int flags)
	{
	return blk_log_writes_co_log(bs, offset, bytes, qiov, flags,
	blk_log_writes_co_do_file_pwritev, 0, false);
	}

	static int coroutine_fn
	blk_log_writes_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int bytes,
	BdrvRequestFlags flags)
	{
	return blk_log_writes_co_log(bs, offset, bytes, NULL, flags,
	blk_log_writes_co_do_file_pwrite_zeroes, 0,
	true);
	}

	static int coroutine_fn blk_log_writes_co_flush_to_disk(BlockDriverState *bs)
	{
	return blk_log_writes_co_log(bs, 0, 0, NULL, 0,
	blk_log_writes_co_do_file_flush,
	LOG_FLUSH_FLAG, false);
	}

	static int coroutine_fn
	blk_log_writes_co_pdiscard(BlockDriverState *bs, int64_t offset, int count)
	{
	return blk_log_writes_co_log(bs, offset, count, NULL, 0,
	blk_log_writes_co_do_file_pdiscard,
	LOG_DISCARD_FLAG, false);
	}

	static const char *const blk_log_writes_strong_runtime_opts[] = {
	"log-append",
	"log-sector-size",

	NULL
	};

	static BlockDriver bdrv_blk_log_writes = {
	.format_name = "blklogwrites",
	.instance_size = sizeof(BDRVBlkLogWritesState),

	.bdrv_open = blk_log_writes_open,
	.bdrv_close = blk_log_writes_close,
	.bdrv_getlength = blk_log_writes_getlength,
	.bdrv_child_perm = blk_log_writes_child_perm,
	.bdrv_refresh_limits = blk_log_writes_refresh_limits,

	.bdrv_co_preadv = blk_log_writes_co_preadv,
	.bdrv_co_pwritev = blk_log_writes_co_pwritev,
	.bdrv_co_pwrite_zeroes = blk_log_writes_co_pwrite_zeroes,
	.bdrv_co_flush_to_disk = blk_log_writes_co_flush_to_disk,
	.bdrv_co_pdiscard = blk_log_writes_co_pdiscard,
	.bdrv_co_block_status = bdrv_co_block_status_from_file,

	.is_filter = true,
	.strong_runtime_opts = blk_log_writes_strong_runtime_opts,
	};

	static void bdrv_blk_log_writes_init(void)
	{
	bdrv_register(&bdrv_blk_log_writes);
	}

	block_init(bdrv_blk_log_writes_init);