[Qemu-devel] [PATCH v3 9/9] block: vhdx write support

[Jeff Cody]

This adds support for writing to VHDX image files, using coroutines.
Writes into the BAT table goes through the VHDX log.  Currently, BAT
table writes occur when expanding a dynamic VHDX file, and allocating a
new BAT entry.

Signed-off-by: Jeff Cody <address@hidden>
---
 block/vhdx.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 148 insertions(+), 2 deletions(-)

diff --git a/block/vhdx.c b/block/vhdx.c
index dabd688..c97955a 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -833,7 +833,7 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, 
int flags)
         }
     }
 
-    /* TODO: differencing files, write */
+    /* TODO: differencing files */
 
     return 0;
 fail:
@@ -965,7 +965,43 @@ exit:
     return ret;
 }
 
+/*
+ * Allocate a new payload block at the end of the file.
+ *
+ * Allocation will happen at 1MB alignment inside the file
+ *
+ * Returns the file offset start of the new payload block
+ */
+static int vhdx_allocate_block(BlockDriverState *bs, BDRVVHDXState *s,
+                                    uint64_t *new_offset)
+{
+    *new_offset = bdrv_getlength(bs->file);
+
+    /* per the spec, the address for a block is in units of 1MB */
+    *new_offset = ROUND_UP(*new_offset, 1024*1024);
+
+    return bdrv_truncate(bs->file, *new_offset + s->block_size);
+}
+
+/*
+ * Update the BAT tablet entry with the new file offset, and the new entry
+ * state */
+static void vhdx_update_bat_table_entry(BlockDriverState *bs, BDRVVHDXState *s,
+                                       VHDXSectorInfo *sinfo,
+                                       uint64_t *bat_entry,
+                                       uint64_t *bat_offset, int state)
+{
+    /* The BAT entry is a uint64, with 44 bits for the file offset in units of
+     * 1MB, and 3 bits for the block state. */
+    s->bat[sinfo->bat_idx]  = ((sinfo->file_offset>>20) <<
+                               VHDX_BAT_FILE_OFF_BITS);
 
+    s->bat[sinfo->bat_idx] |= state & VHDX_BAT_STATE_BIT_MASK;
+
+    *bat_entry = cpu_to_le64(s->bat[sinfo->bat_idx]);
+    *bat_offset = s->bat_offset + sinfo->bat_idx * sizeof(VHDXBatEntry);
+
+}
 
 /* Per the spec, on the first write of guest-visible data to the file the
  * data write guid must be updated in the header */
@@ -982,7 +1018,117 @@ int vhdx_user_visible_write(BlockDriverState *bs, 
BDRVVHDXState *s)
 static coroutine_fn int vhdx_co_writev(BlockDriverState *bs, int64_t 
sector_num,
                                       int nb_sectors, QEMUIOVector *qiov)
 {
-    return -ENOTSUP;
+    int ret = -ENOTSUP;
+    BDRVVHDXState *s = bs->opaque;
+    VHDXSectorInfo sinfo;
+    uint64_t bytes_done = 0;
+    uint64_t bat_entry = 0;
+    uint64_t bat_entry_offset = 0;
+    bool bat_update;
+    QEMUIOVector hd_qiov;
+
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+
+    qemu_co_mutex_lock(&s->lock);
+
+    ret = vhdx_user_visible_write(bs, s);
+    if (ret < 0) {
+        goto exit;
+    }
+
+    while (nb_sectors > 0) {
+        if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
+            /* not supported yet */
+            ret = -ENOTSUP;
+            goto exit;
+        } else {
+            bat_update = false;
+            vhdx_block_translate(s, sector_num, nb_sectors, &sinfo);
+
+            qemu_iovec_reset(&hd_qiov);
+            qemu_iovec_concat(&hd_qiov, qiov,  bytes_done, sinfo.bytes_avail);
+            /* check the payload block state */
+            switch (s->bat[sinfo.bat_idx] & VHDX_BAT_STATE_BIT_MASK) {
+            case PAYLOAD_BLOCK_ZERO:
+                /* in this case, we need to preserve zero writes for
+                 * data that is not part of this write, so we must pad
+                 * the rest of the buffer to zeroes */
+
+                /* if we are on a posix system with ftruncate() that extends
+                 * a file, then it is zero-filled for us.  On Win32, the raw
+                 * layer uses SetFilePointer and SetFileEnd, which does not
+                 * zero fill AFAIK */
+
+                /* TODO: queue another write of zero buffers if the host OS 
does
+                 * not zero-fill on file extension */
+
+                /* fall through */
+            case PAYLOAD_BLOCK_NOT_PRESENT: /* fall through */
+            case PAYLOAD_BLOCK_UNMAPPED:    /* fall through */
+            case PAYLOAD_BLOCK_UNDEFINED:   /* fall through */
+                ret = vhdx_allocate_block(bs, s, &sinfo.file_offset);
+                if (ret < 0) {
+                    goto exit;
+                }
+                /* once we support differencing files, this may also be
+                 * partially present */
+                /* update block state to the newly specified state */
+                vhdx_update_bat_table_entry(bs, s, &sinfo, &bat_entry,
+                                            &bat_entry_offset,
+                                            PAYLOAD_BLOCK_FULL_PRESENT);
+                bat_update = true;
+                /* since we just allocated a block, file_offset is the
+                 * beginning of the payload block. It needs to be the
+                 * write address, which includes the offset into the block */
+                sinfo.file_offset += sinfo.block_offset;
+                /* fall through */
+            case PAYLOAD_BLOCK_FULL_PRESENT:
+                /* if the file offset address is in the header zone,
+                 * there is a problem */
+                if (sinfo.file_offset < (1024*1024)) {
+                    ret = -EFAULT;
+                    goto exit;
+                }
+                /* block exists, so we can just overwrite it */
+                qemu_co_mutex_unlock(&s->lock);
+                ret = bdrv_co_writev(bs->file,
+                                    sinfo.file_offset>>BDRV_SECTOR_BITS,
+                                    sinfo.sectors_avail, &hd_qiov);
+                qemu_co_mutex_lock(&s->lock);
+                if (ret < 0) {
+                    goto exit;
+                }
+                break;
+            case PAYLOAD_BLOCK_PARTIALLY_PRESENT:
+                /* we don't yet support difference files, fall through
+                 * to error */
+            default:
+                ret = -EIO;
+                goto exit;
+                break;
+            }
+
+            if (bat_update) {
+                /* this will update the BAT entry into the log journal, and
+                 * then flush the log journal out to disk */
+                ret =  vhdx_log_write_and_flush(bs, s, &bat_entry,
+                                                sizeof(VHDXBatEntry),
+                                                bat_entry_offset);
+                if (ret < 0) {
+                    goto exit;
+                }
+            }
+
+            nb_sectors -= sinfo.sectors_avail;
+            sector_num += sinfo.sectors_avail;
+            bytes_done += sinfo.bytes_avail;
+
+        }
+    }
+
+exit:
+    qemu_co_mutex_unlock(&s->lock);
+    return ret;
 }
 
 
-- 
1.8.1.4