block: vhdx - add log write support
This adds support for writing to the VHDX log.
For spec details, see VHDX Specification Format v1.00:
https://www.microsoft.com/en-us/download/details.aspx?id=34750
There are a few limitations to this log support:
1.) There is no caching yet
2.) The log is flushed after each entry
The primary write interface, vhdx_log_write_and_flush(), performs a log
write followed by an immediate flush of the log.
As each log entry sector is a minimum of 4KB, partial sector writes are
filled in with data from the disk write destination.
If the current file log GUID is 0, a new GUID is generated and updated
in the header.
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/vhdx-log.c b/block/vhdx-log.c
index 0284729..ee5583c 100644
--- a/block/vhdx-log.c
+++ b/block/vhdx-log.c
@@ -156,6 +156,55 @@
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, buffer_tmp, VHDX_LOG_SECTOR_SIZE);
+ 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)
@@ -726,3 +775,236 @@
}
+
+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;
+ cpu_to_le64s(&desc->leading_bytes);
+ memcpy(sector->data, data, 4084);
+ data += 4084;
+ memcpy(&desc->trailing_bytes, data, 4);
+ cpu_to_le32s(&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;
+ 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 = (offset / VHDX_LOG_SECTOR_SIZE) * 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;
+
+ /* 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 = bdrv_getlength(bs->file),
+ .last_file_offset = bdrv_getlength(bs->file),
+ };
+
+ new_hdr.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 = (VHDXLogDescriptor *) (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, merged_sector,
+ VHDX_LOG_SECTOR_SIZE);
+ 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,
+ merged_sector + trailing_length,
+ VHDX_LOG_SECTOR_SIZE - trailing_length);
+ 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));
+ cpu_to_le32s((uint32_t *)(buffer + 4));
+
+ /* now write to the log */
+ vhdx_log_write_sectors(bs, &s->log, §ors_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 */
+ bdrv_flush(bs);
+ 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 */
+ bdrv_flush(bs);
+ ret = vhdx_log_flush(bs, s, &logs);
+ if (ret < 0) {
+ goto exit;
+ }
+
+ s->log = logs.log;
+
+exit:
+ return ret;
+}
+
