qemu

vhdx-log.c (31006B)

---

 /*
  * Block driver for Hyper-V VHDX Images
  *
  * Copyright (c) 2013 Red Hat, Inc.,
  *
  * Authors:
  *  Jeff Cody <jcody@redhat.com>
  *
  *  This is based on the "VHDX Format Specification v1.00", published 8/25/2012
  *  by Microsoft:
  *      https://www.microsoft.com/en-us/download/details.aspx?id=34750
  *
  * This file covers the functionality of the metadata log writing, parsing, and
  * replay.
  *
  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  * See the COPYING.LIB file in the top-level directory.
  *
  */
 
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "block/block_int.h"
 #include "qemu/error-report.h"
 #include "qemu/bswap.h"
 #include "qemu/memalign.h"
 #include "vhdx.h"
 
 
 typedef struct VHDXLogSequence {
     bool valid;
     uint32_t count;
     VHDXLogEntries log;
     VHDXLogEntryHeader hdr;
 } VHDXLogSequence;
 
 typedef struct VHDXLogDescEntries {
     VHDXLogEntryHeader hdr;
     VHDXLogDescriptor desc[];
 } VHDXLogDescEntries;
 
 static const MSGUID zero_guid = { 0 };
 
 /* The log located on the disk is circular buffer containing
  * sectors of 4096 bytes each.
  *
  * It is assumed for the read/write functions below that the
  * circular buffer scheme uses a 'one sector open' to indicate
  * the buffer is full.  Given the validation methods used for each
  * sector, this method should be compatible with other methods that
  * do not waste a sector.
  */
 
 
 /* Allow peeking at the hdr entry at the beginning of the current
  * read index, without advancing the read index */
 static int vhdx_log_peek_hdr(BlockDriverState *bs, VHDXLogEntries *log,
                              VHDXLogEntryHeader *hdr)
 {
     int ret = 0;
     uint64_t offset;
     uint32_t read;
 
     assert(hdr != NULL);
 
     /* peek is only supported on sector boundaries */
     if (log->read % VHDX_LOG_SECTOR_SIZE) {
         ret = -EFAULT;
         goto exit;
     }
 
     read = log->read;
     /* we are guaranteed that a) log sectors are 4096 bytes,
      * and b) the log length is a multiple of 1MB. So, there
      * is always a round number of sectors in the buffer */
     if ((read + sizeof(VHDXLogEntryHeader)) > log->length) {
         read = 0;
     }
 
     if (read == log->write) {
         ret = -EINVAL;
         goto exit;
     }
 
     offset = log->offset + read;
 
     ret = bdrv_pread(bs->file, offset, sizeof(VHDXLogEntryHeader), hdr, 0);
     if (ret < 0) {
         goto exit;
     }
     vhdx_log_entry_hdr_le_import(hdr);
 
 exit:
     return ret;
 }
 
 /* Index increment for log, based on sector boundaries */
 static int vhdx_log_inc_idx(uint32_t idx, uint64_t length)
 {
     idx += VHDX_LOG_SECTOR_SIZE;
     /* we are guaranteed that a) log sectors are 4096 bytes,
      * and b) the log length is a multiple of 1MB. So, there
      * is always a round number of sectors in the buffer */
     return idx >= length ? 0 : idx;
 }
 
 
 /* Reset the log to empty */
 static void vhdx_log_reset(BlockDriverState *bs, BDRVVHDXState *s)
 {
     MSGUID guid = { 0 };
     s->log.read = s->log.write = 0;
     /* a log guid of 0 indicates an empty log to any parser of v0
      * VHDX logs */
     vhdx_update_headers(bs, s, false, &guid);
 }
 
 /* Reads num_sectors from the log (all log sectors are 4096 bytes),
  * into buffer 'buffer'.  Upon return, *sectors_read will contain
  * the number of sectors successfully read.
  *
  * It is assumed that 'buffer' is already allocated, and of sufficient
  * size (i.e. >= 4096*num_sectors).
  *
  * If 'peek' is true, then the tail (read) pointer for the circular buffer is
  * not modified.
  *
  * 0 is returned on success, -errno otherwise.  */
 static int vhdx_log_read_sectors(BlockDriverState *bs, VHDXLogEntries *log,
                                  uint32_t *sectors_read, void *buffer,
                                  uint32_t num_sectors, bool peek)
 {
     int ret = 0;
     uint64_t offset;
     uint32_t read;
 
     read = log->read;
 
     *sectors_read = 0;
     while (num_sectors) {
         if (read == log->write) {
             /* empty */
             break;
         }
         offset = log->offset + read;
 
         ret = bdrv_pread(bs->file, offset, VHDX_LOG_SECTOR_SIZE, buffer, 0);
         if (ret < 0) {
             goto exit;
         }
         read = vhdx_log_inc_idx(read, log->length);
 
         *sectors_read = *sectors_read + 1;
         num_sectors--;
     }
 
 exit:
     if (!peek) {
         log->read = read;
     }
     return ret;
 }
 
 /* Writes num_sectors to the log (all log sectors are 4096 bytes),
  * from buffer 'buffer'.  Upon return, *sectors_written will contain
  * the number of sectors successfully written.
  *
  * It is assumed that 'buffer' is at least 4096*num_sectors large.
  *
  * 0 is returned on success, -errno otherwise */
 static int vhdx_log_write_sectors(BlockDriverState *bs, VHDXLogEntries *log,
                                   uint32_t *sectors_written, void *buffer,
                                   uint32_t num_sectors)
 {
     int ret = 0;
     uint64_t offset;
     uint32_t write;
     void *buffer_tmp;
     BDRVVHDXState *s = bs->opaque;
 
     ret = vhdx_user_visible_write(bs, s);
     if (ret < 0) {
         goto exit;
     }
 
     write = log->write;
 
     buffer_tmp = buffer;
     while (num_sectors) {
 
         offset = log->offset + write;
         write = vhdx_log_inc_idx(write, log->length);
         if (write == log->read) {
             /* full */
             break;
         }
         ret = bdrv_pwrite(bs->file, offset, VHDX_LOG_SECTOR_SIZE, buffer_tmp,
                           0);
         if (ret < 0) {
             goto exit;
         }
         buffer_tmp += VHDX_LOG_SECTOR_SIZE;
 
         log->write = write;
         *sectors_written = *sectors_written + 1;
         num_sectors--;
     }
 
 exit:
     return ret;
 }
 
 
 /* Validates a log entry header */
 static bool vhdx_log_hdr_is_valid(VHDXLogEntries *log, VHDXLogEntryHeader *hdr,
                                   BDRVVHDXState *s)
 {
     int valid = false;
 
     if (hdr->signature != VHDX_LOG_SIGNATURE) {
         goto exit;
     }
 
     /* if the individual entry length is larger than the whole log
      * buffer, that is obviously invalid */
     if (log->length < hdr->entry_length) {
         goto exit;
     }
 
     /* length of entire entry must be in units of 4KB (log sector size) */
     if (hdr->entry_length % (VHDX_LOG_SECTOR_SIZE)) {
         goto exit;
     }
 
     /* per spec, sequence # must be > 0 */
     if (hdr->sequence_number == 0) {
         goto exit;
     }
 
     /* log entries are only valid if they match the file-wide log guid
      * found in the active header */
     if (!guid_eq(hdr->log_guid, s->headers[s->curr_header]->log_guid)) {
         goto exit;
     }
 
     if (hdr->descriptor_count * sizeof(VHDXLogDescriptor) > hdr->entry_length) {
         goto exit;
     }
 
     valid = true;
 
 exit:
     return valid;
 }
 
 /*
  * Given a log header, this will validate that the descriptors and the
  * corresponding data sectors (if applicable)
  *
  * Validation consists of:
  *      1. Making sure the sequence numbers matches the entry header
  *      2. Verifying a valid signature ('zero' or 'desc' for descriptors)
  *      3. File offset field is a multiple of 4KB
  *      4. If a data descriptor, the corresponding data sector
  *         has its signature ('data') and matching sequence number
  *
  * @desc: the data buffer containing the descriptor
  * @hdr:  the log entry header
  *
  * Returns true if valid
  */
 static bool vhdx_log_desc_is_valid(VHDXLogDescriptor *desc,
                                    VHDXLogEntryHeader *hdr)
 {
     bool ret = false;
 
     if (desc->sequence_number != hdr->sequence_number) {
         goto exit;
     }
     if (desc->file_offset % VHDX_LOG_SECTOR_SIZE) {
         goto exit;
     }
 
     if (desc->signature == VHDX_LOG_ZERO_SIGNATURE) {
         if (desc->zero_length % VHDX_LOG_SECTOR_SIZE == 0) {
             /* valid */
             ret = true;
         }
     } else if (desc->signature == VHDX_LOG_DESC_SIGNATURE) {
             /* valid */
             ret = true;
     }
 
 exit:
     return ret;
 }
 
 
 /* Prior to sector data for a log entry, there is the header
  * and the descriptors referenced in the header:
  *
  * [] = 4KB sector
  *
  * [ hdr, desc ][   desc   ][ ... ][ data ][ ... ]
  *
  * The first sector in a log entry has a 64 byte header, and
  * up to 126 32-byte descriptors.  If more descriptors than
  * 126 are required, then subsequent sectors can have up to 128
  * descriptors.  Each sector is 4KB.  Data follows the descriptor
  * sectors.
  *
  * This will return the number of sectors needed to encompass
  * the passed number of descriptors in desc_cnt.
  *
  * This will never return 0, even if desc_cnt is 0.
  */
 static int vhdx_compute_desc_sectors(uint32_t desc_cnt)
 {
     uint32_t desc_sectors;
 
     desc_cnt += 2; /* account for header in first sector */
     desc_sectors = desc_cnt / 128;
     if (desc_cnt % 128) {
         desc_sectors++;
     }
 
     return desc_sectors;
 }
 
 
 /* Reads the log header, and subsequent descriptors (if any).  This
  * will allocate all the space for buffer, which must be NULL when
  * passed into this function. Each descriptor will also be validated,
  * and error returned if any are invalid. */
 static int vhdx_log_read_desc(BlockDriverState *bs, BDRVVHDXState *s,
                               VHDXLogEntries *log, VHDXLogDescEntries **buffer,
                               bool convert_endian)
 {
     int ret = 0;
     uint32_t desc_sectors;
     uint32_t sectors_read;
     VHDXLogEntryHeader hdr;
     VHDXLogDescEntries *desc_entries = NULL;
     VHDXLogDescriptor desc;
     int i;
 
     assert(*buffer == NULL);
 
     ret = vhdx_log_peek_hdr(bs, log, &hdr);
     if (ret < 0) {
         goto exit;
     }
 
     if (vhdx_log_hdr_is_valid(log, &hdr, s) == false) {
         ret = -EINVAL;
         goto exit;
     }
 
     desc_sectors = vhdx_compute_desc_sectors(hdr.descriptor_count);
     desc_entries = qemu_try_blockalign(bs->file->bs,
                                        desc_sectors * VHDX_LOG_SECTOR_SIZE);
     if (desc_entries == NULL) {
         ret = -ENOMEM;
         goto exit;
     }
 
     ret = vhdx_log_read_sectors(bs, log, &sectors_read, desc_entries,
                                 desc_sectors, false);
     if (ret < 0) {
         goto free_and_exit;
     }
     if (sectors_read != desc_sectors) {
         ret = -EINVAL;
         goto free_and_exit;
     }
 
     /* put in proper endianness, and validate each desc */
     for (i = 0; i < hdr.descriptor_count; i++) {
         desc = desc_entries->desc[i];
         vhdx_log_desc_le_import(&desc);
         if (convert_endian) {
             desc_entries->desc[i] = desc;
         }
         if (vhdx_log_desc_is_valid(&desc, &hdr) == false) {
             ret = -EINVAL;
             goto free_and_exit;
         }
     }
     if (convert_endian) {
         desc_entries->hdr = hdr;
     }
 
     *buffer = desc_entries;
     goto exit;
 
 free_and_exit:
     qemu_vfree(desc_entries);
 exit:
     return ret;
 }
 
 
 /* Flushes the descriptor described by desc to the VHDX image file.
  * If the descriptor is a data descriptor, than 'data' must be non-NULL,
  * and >= 4096 bytes (VHDX_LOG_SECTOR_SIZE), containing the data to be
  * written.
  *
  * Verification is performed to make sure the sequence numbers of a data
  * descriptor match the sequence number in the desc.
  *
  * For a zero descriptor, it may describe multiple sectors to fill with zeroes.
  * In this case, it should be noted that zeroes are written to disk, and the
  * image file is not extended as a sparse file.  */
 static int vhdx_log_flush_desc(BlockDriverState *bs, VHDXLogDescriptor *desc,
                                VHDXLogDataSector *data)
 {
     int ret = 0;
     uint64_t seq, file_offset;
     uint32_t offset = 0;
     void *buffer = NULL;
     uint64_t count = 1;
     int i;
 
     buffer = qemu_blockalign(bs, VHDX_LOG_SECTOR_SIZE);
 
     if (desc->signature == VHDX_LOG_DESC_SIGNATURE) {
         /* data sector */
         if (data == NULL) {
             ret = -EFAULT;
             goto exit;
         }
 
         /* The sequence number of the data sector must match that
          * in the descriptor */
         seq = data->sequence_high;
         seq <<= 32;
         seq |= data->sequence_low & 0xffffffff;
 
         if (seq != desc->sequence_number) {
             ret = -EINVAL;
             goto exit;
         }
 
         /* Each data sector is in total 4096 bytes, however the first
          * 8 bytes, and last 4 bytes, are located in the descriptor */
         memcpy(buffer, &desc->leading_bytes, 8);
         offset += 8;
 
         memcpy(buffer+offset, data->data, 4084);
         offset += 4084;
 
         memcpy(buffer+offset, &desc->trailing_bytes, 4);
 
     } else if (desc->signature == VHDX_LOG_ZERO_SIGNATURE) {
         /* write 'count' sectors of sector */
         memset(buffer, 0, VHDX_LOG_SECTOR_SIZE);
         count = desc->zero_length / VHDX_LOG_SECTOR_SIZE;
     } else {
         error_report("Invalid VHDX log descriptor entry signature 0x%" PRIx32,
                       desc->signature);
         ret = -EINVAL;
         goto exit;
     }
 
     file_offset = desc->file_offset;
 
     /* count is only > 1 if we are writing zeroes */
     for (i = 0; i < count; i++) {
         ret = bdrv_pwrite_sync(bs->file, file_offset, VHDX_LOG_SECTOR_SIZE,
                                buffer, 0);
         if (ret < 0) {
             goto exit;
         }
         file_offset += VHDX_LOG_SECTOR_SIZE;
     }
 
 exit:
     qemu_vfree(buffer);
     return ret;
 }
 
 /* Flush the entire log (as described by 'logs') to the VHDX image
  * file, and then set the log to 'empty' status once complete.
  *
  * The log entries should be validate prior to flushing */
 static int vhdx_log_flush(BlockDriverState *bs, BDRVVHDXState *s,
                           VHDXLogSequence *logs)
 {
     int ret = 0;
     int i;
     uint32_t cnt, sectors_read;
     uint64_t new_file_size;
     void *data = NULL;
     int64_t file_length;
     VHDXLogDescEntries *desc_entries = NULL;
     VHDXLogEntryHeader hdr_tmp = { 0 };
 
     cnt = logs->count;
 
     data = qemu_blockalign(bs, VHDX_LOG_SECTOR_SIZE);
 
     ret = vhdx_user_visible_write(bs, s);
     if (ret < 0) {
         goto exit;
     }
 
     /* each iteration represents one log sequence, which may span multiple
      * sectors */
     while (cnt--) {
         ret = vhdx_log_peek_hdr(bs, &logs->log, &hdr_tmp);
         if (ret < 0) {
             goto exit;
         }
         file_length = bdrv_getlength(bs->file->bs);
         if (file_length < 0) {
             ret = file_length;
             goto exit;
         }
         /* if the log shows a FlushedFileOffset larger than our current file
          * size, then that means the file has been truncated / corrupted, and
          * we must refused to open it / use it */
         if (hdr_tmp.flushed_file_offset > file_length) {
             ret = -EINVAL;
             goto exit;
         }
 
         ret = vhdx_log_read_desc(bs, s, &logs->log, &desc_entries, true);
         if (ret < 0) {
             goto exit;
         }
 
         for (i = 0; i < desc_entries->hdr.descriptor_count; i++) {
             if (desc_entries->desc[i].signature == VHDX_LOG_DESC_SIGNATURE) {
                 /* data sector, so read a sector to flush */
                 ret = vhdx_log_read_sectors(bs, &logs->log, &sectors_read,
                                             data, 1, false);
                 if (ret < 0) {
                     goto exit;
                 }
                 if (sectors_read != 1) {
                     ret = -EINVAL;
                     goto exit;
                 }
                 vhdx_log_data_le_import(data);
             }
 
             ret = vhdx_log_flush_desc(bs, &desc_entries->desc[i], data);
             if (ret < 0) {
                 goto exit;
             }
         }
         if (file_length < desc_entries->hdr.last_file_offset) {
             new_file_size = desc_entries->hdr.last_file_offset;
             if (new_file_size % (1 * MiB)) {
                 /* round up to nearest 1MB boundary */
                 new_file_size = QEMU_ALIGN_UP(new_file_size, MiB);
                 if (new_file_size > INT64_MAX) {
                     ret = -EINVAL;
                     goto exit;
                 }
                 ret = bdrv_truncate(bs->file, new_file_size, false,
                                     PREALLOC_MODE_OFF, 0, NULL);
                 if (ret < 0) {
                     goto exit;
                 }
             }
         }
         qemu_vfree(desc_entries);
         desc_entries = NULL;
     }
 
     ret = bdrv_flush(bs);
     if (ret < 0) {
         goto exit;
     }
     /* once the log is fully flushed, indicate that we have an empty log
      * now.  This also sets the log guid to 0, to indicate an empty log */
     vhdx_log_reset(bs, s);
 
 exit:
     qemu_vfree(data);
     qemu_vfree(desc_entries);
     return ret;
 }
 
 static int vhdx_validate_log_entry(BlockDriverState *bs, BDRVVHDXState *s,
                                    VHDXLogEntries *log, uint64_t seq,
                                    bool *valid, VHDXLogEntryHeader *entry)
 {
     int ret = 0;
     VHDXLogEntryHeader hdr;
     void *buffer = NULL;
     uint32_t i, desc_sectors, total_sectors, crc;
     uint32_t sectors_read = 0;
     VHDXLogDescEntries *desc_buffer = NULL;
 
     *valid = false;
 
     ret = vhdx_log_peek_hdr(bs, log, &hdr);
     if (ret < 0) {
         goto inc_and_exit;
     }
 
     if (vhdx_log_hdr_is_valid(log, &hdr, s) == false) {
         goto inc_and_exit;
     }
 
     if (seq > 0) {
         if (hdr.sequence_number != seq + 1) {
             goto inc_and_exit;
         }
     }
 
     desc_sectors = vhdx_compute_desc_sectors(hdr.descriptor_count);
 
     /* Read all log sectors, and calculate log checksum */
 
     total_sectors = hdr.entry_length / VHDX_LOG_SECTOR_SIZE;
 
 
     /* read_desc() will increment the read idx */
     ret = vhdx_log_read_desc(bs, s, log, &desc_buffer, false);
     if (ret < 0) {
         goto free_and_exit;
     }
 
     crc = vhdx_checksum_calc(0xffffffff, (void *)desc_buffer,
                             desc_sectors * VHDX_LOG_SECTOR_SIZE, 4);
     crc ^= 0xffffffff;
 
     buffer = qemu_blockalign(bs, VHDX_LOG_SECTOR_SIZE);
     if (total_sectors > desc_sectors) {
         for (i = 0; i < total_sectors - desc_sectors; i++) {
             sectors_read = 0;
             ret = vhdx_log_read_sectors(bs, log, &sectors_read, buffer,
                                         1, false);
             if (ret < 0 || sectors_read != 1) {
                 goto free_and_exit;
             }
             crc = vhdx_checksum_calc(crc, buffer, VHDX_LOG_SECTOR_SIZE, -1);
             crc ^= 0xffffffff;
         }
     }
     crc ^= 0xffffffff;
     if (crc != hdr.checksum) {
         goto free_and_exit;
     }
 
     *valid = true;
     *entry = hdr;
     goto free_and_exit;
 
 inc_and_exit:
     log->read = vhdx_log_inc_idx(log->read, log->length);
 
 free_and_exit:
     qemu_vfree(buffer);
     qemu_vfree(desc_buffer);
     return ret;
 }
 
 /* Search through the log circular buffer, and find the valid, active
  * log sequence, if any exists
  * */
 static int vhdx_log_search(BlockDriverState *bs, BDRVVHDXState *s,
                            VHDXLogSequence *logs)
 {
     int ret = 0;
     uint32_t tail;
     bool seq_valid = false;
     VHDXLogSequence candidate = { 0 };
     VHDXLogEntryHeader hdr = { 0 };
     VHDXLogEntries curr_log;
 
     memcpy(&curr_log, &s->log, sizeof(VHDXLogEntries));
     curr_log.write = curr_log.length;   /* assume log is full */
     curr_log.read = 0;
 
 
     /* now we will go through the whole log sector by sector, until
      * we find a valid, active log sequence, or reach the end of the
      * log buffer */
     for (;;) {
         uint64_t curr_seq = 0;
         VHDXLogSequence current = { 0 };
 
         tail = curr_log.read;
 
         ret = vhdx_validate_log_entry(bs, s, &curr_log, curr_seq,
                                       &seq_valid, &hdr);
         if (ret < 0) {
             goto exit;
         }
 
         if (seq_valid) {
             current.valid     = true;
             current.log       = curr_log;
             current.log.read  = tail;
             current.log.write = curr_log.read;
             current.count     = 1;
             current.hdr       = hdr;
 
 
             for (;;) {
                 ret = vhdx_validate_log_entry(bs, s, &curr_log, curr_seq,
                                               &seq_valid, &hdr);
                 if (ret < 0) {
                     goto exit;
                 }
                 if (seq_valid == false) {
                     break;
                 }
                 current.log.write = curr_log.read;
                 current.count++;
 
                 curr_seq = hdr.sequence_number;
             }
         }
 
         if (current.valid) {
             if (candidate.valid == false ||
                 current.hdr.sequence_number > candidate.hdr.sequence_number) {
                 candidate = current;
             }
         }
 
         if (curr_log.read < tail) {
             break;
         }
     }
 
     *logs = candidate;
 
     if (candidate.valid) {
         /* this is the next sequence number, for writes */
         s->log.sequence = candidate.hdr.sequence_number + 1;
     }
 
 
 exit:
     return ret;
 }
 
 /* Parse the replay log.  Per the VHDX spec, if the log is present
  * it must be replayed prior to opening the file, even read-only.
  *
  * If read-only, we must replay the log in RAM (or refuse to open
  * a dirty VHDX file read-only) */
 int vhdx_parse_log(BlockDriverState *bs, BDRVVHDXState *s, bool *flushed,
                    Error **errp)
 {
     int ret = 0;
     VHDXHeader *hdr;
     VHDXLogSequence logs = { 0 };
 
     hdr = s->headers[s->curr_header];
 
     *flushed = false;
 
     /* s->log.hdr is freed in vhdx_close() */
     if (s->log.hdr == NULL) {
         s->log.hdr = qemu_blockalign(bs, sizeof(VHDXLogEntryHeader));
     }
 
     s->log.offset = hdr->log_offset;
     s->log.length = hdr->log_length;
 
     if (s->log.offset < VHDX_LOG_MIN_SIZE ||
         s->log.offset % VHDX_LOG_MIN_SIZE) {
         ret = -EINVAL;
         goto exit;
     }
 
     /* per spec, only log version of 0 is supported */
     if (hdr->log_version != 0) {
         ret = -EINVAL;
         goto exit;
     }
 
     /* If either the log guid, or log length is zero,
      * then a replay log is not present */
     if (guid_eq(hdr->log_guid, zero_guid)) {
         goto exit;
     }
 
     if (hdr->log_length == 0) {
         goto exit;
     }
 
     if (hdr->log_length % VHDX_LOG_MIN_SIZE) {
         ret = -EINVAL;
         goto exit;
     }
 
 
     /* The log is present, we need to find if and where there is an active
      * sequence of valid entries present in the log.  */
 
     ret = vhdx_log_search(bs, s, &logs);
     if (ret < 0) {
         goto exit;
     }
 
     if (logs.valid) {
         if (bdrv_is_read_only(bs)) {
             bdrv_refresh_filename(bs);
             ret = -EPERM;
             error_setg(errp,
                        "VHDX image file '%s' opened read-only, but "
                        "contains a log that needs to be replayed",
                        bs->filename);
             error_append_hint(errp,  "To replay the log, run:\n"
                               "qemu-img check -r all '%s'\n",
                               bs->filename);
             goto exit;
         }
         /* now flush the log */
         ret = vhdx_log_flush(bs, s, &logs);
         if (ret < 0) {
             goto exit;
         }
         *flushed = true;
     }
 
 
 exit:
     return ret;
 }
 
 
 
 static void vhdx_log_raw_to_le_sector(VHDXLogDescriptor *desc,
                                       VHDXLogDataSector *sector, void *data,
                                       uint64_t seq)
 {
     /* 8 + 4084 + 4 = 4096, 1 log sector */
     memcpy(&desc->leading_bytes, data, 8);
     data += 8;
     desc->leading_bytes = cpu_to_le64(desc->leading_bytes);
     memcpy(sector->data, data, 4084);
     data += 4084;
     memcpy(&desc->trailing_bytes, data, 4);
     desc->trailing_bytes = cpu_to_le32(desc->trailing_bytes);
     data += 4;
 
     sector->sequence_high  = (uint32_t) (seq >> 32);
     sector->sequence_low   = (uint32_t) (seq & 0xffffffff);
     sector->data_signature = VHDX_LOG_DATA_SIGNATURE;
 
     vhdx_log_desc_le_export(desc);
     vhdx_log_data_le_export(sector);
 }
 
 
 static int vhdx_log_write(BlockDriverState *bs, BDRVVHDXState *s,
                           void *data, uint32_t length, uint64_t offset)
 {
     int ret = 0;
     void *buffer = NULL;
     void *merged_sector = NULL;
     void *data_tmp, *sector_write;
     unsigned int i;
     int sector_offset;
     uint32_t desc_sectors, sectors, total_length;
     uint32_t sectors_written = 0;
     uint32_t aligned_length;
     uint32_t leading_length = 0;
     uint32_t trailing_length = 0;
     uint32_t partial_sectors = 0;
     uint32_t bytes_written = 0;
     uint64_t file_offset;
     int64_t file_length;
     VHDXHeader *header;
     VHDXLogEntryHeader new_hdr;
     VHDXLogDescriptor *new_desc = NULL;
     VHDXLogDataSector *data_sector = NULL;
     MSGUID new_guid = { 0 };
 
     header = s->headers[s->curr_header];
 
     /* need to have offset read data, and be on 4096 byte boundary */
 
     if (length > header->log_length) {
         /* no log present.  we could create a log here instead of failing */
         ret = -EINVAL;
         goto exit;
     }
 
     if (guid_eq(header->log_guid, zero_guid)) {
         vhdx_guid_generate(&new_guid);
         vhdx_update_headers(bs, s, false, &new_guid);
     } else {
         /* currently, we require that the log be flushed after
          * every write. */
         ret = -ENOTSUP;
         goto exit;
     }
 
     /* 0 is an invalid sequence number, but may also represent the first
      * log write (or a wrapped seq) */
     if (s->log.sequence == 0) {
         s->log.sequence = 1;
     }
 
     sector_offset = offset % VHDX_LOG_SECTOR_SIZE;
     file_offset = QEMU_ALIGN_DOWN(offset, VHDX_LOG_SECTOR_SIZE);
 
     aligned_length = length;
 
     /* add in the unaligned head and tail bytes */
     if (sector_offset) {
         leading_length = (VHDX_LOG_SECTOR_SIZE - sector_offset);
         leading_length = leading_length > length ? length : leading_length;
         aligned_length -= leading_length;
         partial_sectors++;
     }
 
     sectors = aligned_length / VHDX_LOG_SECTOR_SIZE;
     trailing_length = aligned_length - (sectors * VHDX_LOG_SECTOR_SIZE);
     if (trailing_length) {
         partial_sectors++;
     }
 
     sectors += partial_sectors;
 
     file_length = bdrv_getlength(bs->file->bs);
     if (file_length < 0) {
         ret = file_length;
         goto exit;
     }
 
     /* sectors is now how many sectors the data itself takes, not
      * including the header and descriptor metadata */
 
     new_hdr = (VHDXLogEntryHeader) {
                 .signature           = VHDX_LOG_SIGNATURE,
                 .tail                = s->log.tail,
                 .sequence_number     = s->log.sequence,
                 .descriptor_count    = sectors,
                 .reserved            = 0,
                 .flushed_file_offset = file_length,
                 .last_file_offset    = file_length,
                 .log_guid            = header->log_guid,
               };
 
 
     desc_sectors = vhdx_compute_desc_sectors(new_hdr.descriptor_count);
 
     total_length = (desc_sectors + sectors) * VHDX_LOG_SECTOR_SIZE;
     new_hdr.entry_length = total_length;
 
     vhdx_log_entry_hdr_le_export(&new_hdr);
 
     buffer = qemu_blockalign(bs, total_length);
     memcpy(buffer, &new_hdr, sizeof(new_hdr));
 
     new_desc = buffer + sizeof(new_hdr);
     data_sector = buffer + (desc_sectors * VHDX_LOG_SECTOR_SIZE);
     data_tmp = data;
 
     /* All log sectors are 4KB, so for any partial sectors we must
      * merge the data with preexisting data from the final file
      * destination */
     merged_sector = qemu_blockalign(bs, VHDX_LOG_SECTOR_SIZE);
 
     for (i = 0; i < sectors; i++) {
         new_desc->signature       = VHDX_LOG_DESC_SIGNATURE;
         new_desc->sequence_number = s->log.sequence;
         new_desc->file_offset     = file_offset;
 
         if (i == 0 && leading_length) {
             /* partial sector at the front of the buffer */
             ret = bdrv_pread(bs->file, file_offset, VHDX_LOG_SECTOR_SIZE,
                              merged_sector, 0);
             if (ret < 0) {
                 goto exit;
             }
             memcpy(merged_sector + sector_offset, data_tmp, leading_length);
             bytes_written = leading_length;
             sector_write = merged_sector;
         } else if (i == sectors - 1 && trailing_length) {
             /* partial sector at the end of the buffer */
             ret = bdrv_pread(bs->file, file_offset,
                              VHDX_LOG_SECTOR_SIZE - trailing_length,
                              merged_sector + trailing_length, 0);
             if (ret < 0) {
                 goto exit;
             }
             memcpy(merged_sector, data_tmp, trailing_length);
             bytes_written = trailing_length;
             sector_write = merged_sector;
         } else {
             bytes_written = VHDX_LOG_SECTOR_SIZE;
             sector_write = data_tmp;
         }
 
         /* populate the raw sector data into the proper structures,
          * as well as update the descriptor, and convert to proper
          * endianness */
         vhdx_log_raw_to_le_sector(new_desc, data_sector, sector_write,
                                   s->log.sequence);
 
         data_tmp += bytes_written;
         data_sector++;
         new_desc++;
         file_offset += VHDX_LOG_SECTOR_SIZE;
     }
 
     /* checksum covers entire entry, from the log header through the
      * last data sector */
     vhdx_update_checksum(buffer, total_length,
                          offsetof(VHDXLogEntryHeader, checksum));
 
     /* now write to the log */
     ret = vhdx_log_write_sectors(bs, &s->log, &sectors_written, buffer,
                                  desc_sectors + sectors);
     if (ret < 0) {
         goto exit;
     }
 
     if (sectors_written != desc_sectors + sectors) {
         /* instead of failing, we could flush the log here */
         ret = -EINVAL;
         goto exit;
     }
 
     s->log.sequence++;
     /* write new tail */
     s->log.tail = s->log.write;
 
 exit:
     qemu_vfree(buffer);
     qemu_vfree(merged_sector);
     return ret;
 }
 
 /* Perform a log write, and then immediately flush the entire log */
 int vhdx_log_write_and_flush(BlockDriverState *bs, BDRVVHDXState *s,
                              void *data, uint32_t length, uint64_t offset)
 {
     int ret = 0;
     VHDXLogSequence logs = { .valid = true,
                              .count = 1,
                              .hdr = { 0 } };
 
 
     /* Make sure data written (new and/or changed blocks) is stable
      * on disk, before creating log entry */
     ret = bdrv_flush(bs);
     if (ret < 0) {
         goto exit;
     }
 
     ret = vhdx_log_write(bs, s, data, length, offset);
     if (ret < 0) {
         goto exit;
     }
     logs.log = s->log;
 
     /* Make sure log is stable on disk */
     ret = bdrv_flush(bs);
     if (ret < 0) {
         goto exit;
     }
 
     ret = vhdx_log_flush(bs, s, &logs);
     if (ret < 0) {
         goto exit;
     }
 
     s->log = logs.log;
 
 exit:
     return ret;
 }