Patchwork [7/7] block: add write support for VHDX images

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Submitter Jeff Cody
Date March 6, 2013, 2:48 p.m.
Message ID <7aabf75e26ea1d60102fd0e1adfcd104aa3689c8.1362580930.git.jcody@redhat.com>
Download mbox | patch
Permalink /patch/225515/
State New
Headers show

Comments

Jeff Cody - March 6, 2013, 2:48 p.m.
This adds in write support for VHDX images.  This supports writing to
both dynamic and fixed VHDX images.  Differencing images are still
unsupported.

Signed-off-by: Jeff Cody <jcody@redhat.com>
---
 block/vhdx.c | 144 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 142 insertions(+), 2 deletions(-)
Stefan Hajnoczi - March 7, 2013, 3:59 p.m.
On Wed, Mar 06, 2013 at 09:48:43AM -0500, Jeff Cody wrote:
> @@ -958,12 +960,150 @@ 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 */
> +    if (*new_offset % (1024*1024)) {
> +        *new_offset = ((*new_offset >> 20) + 1) << 20;  /* round up to 1MB */
> +    }
> +    return bdrv_truncate(bs->file, *new_offset + s->block_size);
> +}

Is it necessary to resize the file?  Why not just write at EOF to grow
it?

> +/*
> + * Update the BAT tablet entry with the new file offset, and the new entry
> + * state */
> +static int vhdx_update_bat_table_entry(BlockDriverState *bs, BDRVVHDXState *s,
> +                                       vhdx_sector_info *sinfo, int state)
> +{
> +    uint64_t bat_tmp;
> +    uint64_t bat_entry_offset;
> +
> +    /* 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_tmp = cpu_to_le64(s->bat[sinfo->bat_idx]);
> +    bat_entry_offset = s->bat_offset + sinfo->bat_idx * sizeof(vhdx_bat_entry);
> +
> +    return bdrv_pwrite_sync(bs->file, bat_entry_offset, &bat_tmp,
> +                            sizeof(vhdx_bat_entry));
> +}
>  
>  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;
> +    vhdx_sector_info sinfo;
> +    uint64_t bytes_done = 0;
> +    QEMUIOVector hd_qiov;
> +
> +    qemu_iovec_init(&hd_qiov, qiov->niov);
> +
> +    qemu_co_mutex_lock(&s->lock);
> +
> +    /* Per the spec, on the first write of guest-visible data to the file the
> +     * data write guid must be updated in the header */
> +    if (s->first_visible_write) {
> +        s->first_visible_write = false;
> +        vhdx_update_headers(bs, s, true);
> +    }
> +
> +    while (nb_sectors > 0) {
> +        if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
> +            /* not supported yet */
> +            ret = -ENOTSUP;
> +            goto exit;
> +        } else {
> +            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 */
> +                ret = vhdx_update_bat_table_entry(bs, s, &sinfo,
> +                                                  PAYLOAD_BLOCK_FULL_PRESENT);
> +                if (ret < 0) {
> +                    goto exit;
> +                }

The BAT table entry must be written after data is already on disk.
Otherwise a crash partway through would leave the BAT table pointing to
undefined data.

Do you need to use the log to ensure this?
Jeff Cody - March 7, 2013, 4:05 p.m.
On Thu, Mar 07, 2013 at 04:59:05PM +0100, Stefan Hajnoczi wrote:
> On Wed, Mar 06, 2013 at 09:48:43AM -0500, Jeff Cody wrote:
> > @@ -958,12 +960,150 @@ 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 */
> > +    if (*new_offset % (1024*1024)) {
> > +        *new_offset = ((*new_offset >> 20) + 1) << 20;  /* round up to 1MB */
> > +    }
> > +    return bdrv_truncate(bs->file, *new_offset + s->block_size);
> > +}
> 
> Is it necessary to resize the file?  Why not just write at EOF to grow
> it?
> 

After the recent bdrv_truncate() discussion, I think that may be best.

> > +/*
> > + * Update the BAT tablet entry with the new file offset, and the new entry
> > + * state */
> > +static int vhdx_update_bat_table_entry(BlockDriverState *bs, BDRVVHDXState *s,
> > +                                       vhdx_sector_info *sinfo, int state)
> > +{
> > +    uint64_t bat_tmp;
> > +    uint64_t bat_entry_offset;
> > +
> > +    /* 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_tmp = cpu_to_le64(s->bat[sinfo->bat_idx]);
> > +    bat_entry_offset = s->bat_offset + sinfo->bat_idx * sizeof(vhdx_bat_entry);
> > +
> > +    return bdrv_pwrite_sync(bs->file, bat_entry_offset, &bat_tmp,
> > +                            sizeof(vhdx_bat_entry));
> > +}
> >  
> >  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;
> > +    vhdx_sector_info sinfo;
> > +    uint64_t bytes_done = 0;
> > +    QEMUIOVector hd_qiov;
> > +
> > +    qemu_iovec_init(&hd_qiov, qiov->niov);
> > +
> > +    qemu_co_mutex_lock(&s->lock);
> > +
> > +    /* Per the spec, on the first write of guest-visible data to the file the
> > +     * data write guid must be updated in the header */
> > +    if (s->first_visible_write) {
> > +        s->first_visible_write = false;
> > +        vhdx_update_headers(bs, s, true);
> > +    }
> > +
> > +    while (nb_sectors > 0) {
> > +        if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
> > +            /* not supported yet */
> > +            ret = -ENOTSUP;
> > +            goto exit;
> > +        } else {
> > +            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 */
> > +                ret = vhdx_update_bat_table_entry(bs, s, &sinfo,
> > +                                                  PAYLOAD_BLOCK_FULL_PRESENT);
> > +                if (ret < 0) {
> > +                    goto exit;
> > +                }
> 
> The BAT table entry must be written after data is already on disk.
> Otherwise a crash partway through would leave the BAT table pointing to
> undefined data.
> 
> Do you need to use the log to ensure this?

Yes, indeed.  The log support is what I am working on now - all
metadata and BAT writes are supposed to go through the log, for this
reason.  The next version will have log support, and so I will use
that for the BAT writes (and any other metadata writes, except the
header).

Patch

diff --git a/block/vhdx.c b/block/vhdx.c
index 13d1e7f..316a5d8 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -165,6 +165,7 @@  typedef struct BDRVVHDXState {
     vhdx_bat_entry *bat;
     uint64_t bat_offset;
 
+    bool first_visible_write;
     ms_guid session_guid;
 
 
@@ -782,6 +783,7 @@  static int vhdx_open(BlockDriverState *bs, int flags)
     int i;
 
     s->bat = NULL;
+    s->first_visible_write = true;
 
     qemu_co_mutex_init(&s->lock);
 
@@ -829,7 +831,7 @@  static int vhdx_open(BlockDriverState *bs, int flags)
         vhdx_update_headers(bs, s, false);
     }
 
-    /* TODO: differencing files, write */
+    /* TODO: differencing files */
 
     return 0;
 fail:
@@ -958,12 +960,150 @@  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 */
+    if (*new_offset % (1024*1024)) {
+        *new_offset = ((*new_offset >> 20) + 1) << 20;  /* round up to 1MB */
+    }
+    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 int vhdx_update_bat_table_entry(BlockDriverState *bs, BDRVVHDXState *s,
+                                       vhdx_sector_info *sinfo, int state)
+{
+    uint64_t bat_tmp;
+    uint64_t bat_entry_offset;
+
+    /* 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_tmp = cpu_to_le64(s->bat[sinfo->bat_idx]);
+    bat_entry_offset = s->bat_offset + sinfo->bat_idx * sizeof(vhdx_bat_entry);
+
+    return bdrv_pwrite_sync(bs->file, bat_entry_offset, &bat_tmp,
+                            sizeof(vhdx_bat_entry));
+}
 
 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;
+    vhdx_sector_info sinfo;
+    uint64_t bytes_done = 0;
+    QEMUIOVector hd_qiov;
+
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+
+    qemu_co_mutex_lock(&s->lock);
+
+    /* Per the spec, on the first write of guest-visible data to the file the
+     * data write guid must be updated in the header */
+    if (s->first_visible_write) {
+        s->first_visible_write = false;
+        vhdx_update_headers(bs, s, true);
+    }
+
+    while (nb_sectors > 0) {
+        if (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) {
+            /* not supported yet */
+            ret = -ENOTSUP;
+            goto exit;
+        } else {
+            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 */
+                ret = vhdx_update_bat_table_entry(bs, s, &sinfo,
+                                                  PAYLOAD_BLOCK_FULL_PRESENT);
+                if (ret < 0) {
+                    goto exit;
+                }
+                /* 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;
+            }
+
+            nb_sectors -= sinfo.sectors_avail;
+            sector_num += sinfo.sectors_avail;
+            bytes_done += sinfo.bytes_avail;
+
+        }
+    }
+
+exit:
+    qemu_co_mutex_unlock(&s->lock);
+    return ret;
 }