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>

block/vhdx-log.c

@@ -156,6 +156,55 @@ exit:
     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 @@ exit:
 }
 
 
+
+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, &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 */
+    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;
+}
+

block/vhdx.h

@@ -398,6 +398,9 @@ bool vhdx_checksum_is_valid(uint8_t *buf, size_t size, int crc_offset);
 
 int vhdx_parse_log(BlockDriverState *bs, BDRVVHDXState *s, bool *flushed);
 
+int vhdx_log_write_and_flush(BlockDriverState *bs, BDRVVHDXState *s,
+                             void *data, uint32_t length, uint64_t offset);
+
 static inline void leguid_to_cpus(MSGUID *guid)
 {
     le32_to_cpus(&guid->data1);