Re: [Qemu-devel] [v2 Patch 2/9]block: raw-posix image file reopen

[Jeff Cody]

On 07/30/2012 05:34 PM, Supriya Kannery wrote:
> raw-posix driver changes for bdrv_reopen_xx functions to
> safely reopen image files. Reopening of image files while 
> changing hostcache dynamically is handled here.
> 
> Signed-off-by: Supriya Kannery <address@hidden>
> 
> ---
> Index: qemu/block/raw.c
> ===================================================================
> --- qemu.orig/block/raw.c
> +++ qemu/block/raw.c
> @@ -9,6 +9,22 @@ static int raw_open(BlockDriverState *bs
>      return 0;
>  }
>  
> +static int raw_reopen_prepare(BlockDriverState *bs, BDRVReopenState **prs,
> +                              int flags)
> +{
> +    return bdrv_reopen_prepare(bs->file, prs, flags);
> +}
> +
> +static void raw_reopen_commit(BlockDriverState *bs, BDRVReopenState *rs)
> +{
> +    bdrv_reopen_commit(bs->file, rs);
> +}
> +
> +static void raw_reopen_abort(BlockDriverState *bs, BDRVReopenState *rs)
> +{
> +    bdrv_reopen_abort(bs->file, rs);
> +}
> +

I think the above should be stubs that do nothing (or, alternatively,
are not present at all), if we have the reopen() do the bs->file
reopen() (which is needed for qcow2 - see my comments for patch 1/9)

>  static int coroutine_fn raw_co_readv(BlockDriverState *bs, int64_t 
> sector_num,
>                                       int nb_sectors, QEMUIOVector *qiov)
>  {
> @@ -113,6 +129,10 @@ static BlockDriver bdrv_raw = {
>      .instance_size      = 1,
>  
>      .bdrv_open          = raw_open,
> +    .bdrv_reopen_prepare
> +                        = raw_reopen_prepare,
> +    .bdrv_reopen_commit = raw_reopen_commit,
> +    .bdrv_reopen_abort  = raw_reopen_abort,
>      .bdrv_close         = raw_close,
>  
>      .bdrv_co_readv          = raw_co_readv,
> Index: qemu/block/raw-posix.c
> ===================================================================
> --- qemu.orig/block/raw-posix.c
> +++ qemu/block/raw-posix.c
> @@ -140,8 +140,15 @@ typedef struct BDRVRawState {
>  #endif
>  } BDRVRawState;
>  
> +typedef struct BDRVRawReopenState {
> +    BDRVReopenState reopen_state;
> +    BDRVRawState *stash_s;
> +} BDRVRawReopenState;
> +
>  static int fd_open(BlockDriverState *bs);
>  static int64_t raw_getlength(BlockDriverState *bs);
> +static void raw_stash_state(BDRVRawState *stashed_state, BDRVRawState *s);
> +static void raw_revert_state(BDRVRawState *s, BDRVRawState *stashed_state);
>  
>  #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
>  static int cdrom_reopen(BlockDriverState *bs);
> @@ -283,6 +290,117 @@ static int raw_open(BlockDriverState *bs
>      return raw_open_common(bs, filename, flags, 0);
>  }
>  
> +static int raw_reopen_prepare(BlockDriverState *bs, BDRVReopenState **prs,
> +                              int flags)
> +{
> +    BDRVRawReopenState *raw_rs = g_malloc0(sizeof(BDRVRawReopenState));
> +    BDRVRawState *s = bs->opaque;
> +    int ret = 0;
> +
> +    raw_rs->reopen_state.bs = bs;
> +
> +    /* stash state before reopen */
> +    raw_rs->stash_s = g_malloc0(sizeof(BDRVRawState));
> +    raw_stash_state(raw_rs->stash_s, s);
> +    s->fd = dup3(raw_rs->stash_s->fd, s->fd, O_CLOEXEC);
> +
> +    *prs = &(raw_rs->reopen_state);
> +
> +    /* Flags that can be set using fcntl */
> +    int fcntl_flags = BDRV_O_NOCACHE;
> +
> +    if ((bs->open_flags & ~fcntl_flags) == (flags & ~fcntl_flags)) {
> +        if ((flags & BDRV_O_NOCACHE)) {
> +            s->open_flags |= O_DIRECT;
> +        } else {
> +            s->open_flags &= ~O_DIRECT;
> +        }
> +        ret = fcntl_setfl(s->fd, s->open_flags);
> +    } else {
> +
> +        /* close and reopen using new flags */
> +        bs->drv->bdrv_close(bs);
> +        ret = bs->drv->bdrv_file_open(bs, bs->filename, flags);

This worries me, in that we close the BDS and then try
to reopen it.  At this point, if the bdrv_file_open() fails, we have no
recovery mechanism.

Maybe we could try to do something like a bdrv_file_open() into a new BDS
before we close, followed by something akin to a bdrv_swap() /
bdrv_append() if the new bdrv_file_open() was successful, and then do
the close on the original.  On failure, just abandon the new BDS.

> +    }
> +    return ret;
> +}
> +
> +static void raw_reopen_commit(BlockDriverState *bs, BDRVReopenState *rs)
> +{
> +    BDRVRawReopenState *raw_rs;
> +
> +    raw_rs = container_of(rs, BDRVRawReopenState, reopen_state);
> +
> +    /* clean up stashed state */
> +    close(raw_rs->stash_s->fd);
> +    g_free(raw_rs->stash_s);
> +    g_free(raw_rs);
> +}
> +
> +static void raw_reopen_abort(BlockDriverState *bs, BDRVReopenState *rs)
> +{
> +    BDRVRawReopenState *raw_rs;
> +    BDRVRawState *s = bs->opaque;
> +
> +    raw_rs = container_of(rs, BDRVRawReopenState, reopen_state);
> +
> +    /* revert to stashed state */
> +    if (s->fd != -1) {
> +        close(s->fd);
> +    }
> +    raw_revert_state(s, raw_rs->stash_s);
> +    g_free(raw_rs->stash_s);
> +    g_free(raw_rs);
> +}
> +
> +static void raw_stash_state(BDRVRawState *stashed_s, BDRVRawState *s)
> +{
> +    stashed_s->fd = -1;
> +    stashed_s->type = s->type;
> +    stashed_s->open_flags = s->open_flags;
> +#if defined(__linux__)
> +    /* linux floppy specific */
> +    stashed_s->fd_open_time = s->fd_open_time;
> +    stashed_s->fd_error_time = s->fd_error_time;
> +    stashed_s->fd_got_error = s->fd_got_error;
> +    stashed_s->fd_media_changed = s->fd_media_changed;
> +#endif
> +#ifdef CONFIG_LINUX_AIO
> +    stashed_s->use_aio = s->use_aio;
> +    stashed_s->aio_ctx = s->aio_ctx;
> +#endif
> +    stashed_s->aligned_buf = s->aligned_buf;
> +    stashed_s->aligned_buf_size = s->aligned_buf_size;
> +#ifdef CONFIG_XFS
> +    stashed_s->is_xfs = s->is_xfs;
> +#endif
> +
> +}
> +
> +static void raw_revert_state(BDRVRawState *s, BDRVRawState *stashed_s)
> +{
> +
> +    s->fd = stashed_s->fd;
> +    s->type = stashed_s->type;
> +    s->open_flags = stashed_s->open_flags;
> +#if defined(__linux__)
> +    /* linux floppy specific */
> +    s->fd_open_time = stashed_s->fd_open_time;
> +    s->fd_error_time = stashed_s->fd_error_time;
> +    s->fd_got_error = stashed_s->fd_got_error;
> +    s->fd_media_changed = stashed_s->fd_media_changed;
> +#endif
> +#ifdef CONFIG_LINUX_AIO
> +    s->use_aio = stashed_s->use_aio;
> +    s->aio_ctx = stashed_s->aio_ctx;
> +#endif
> +    s->aligned_buf = stashed_s->aligned_buf;
> +    s->aligned_buf_size = stashed_s->aligned_buf_size;
> +#ifdef CONFIG_XFS
> +    s->is_xfs = stashed_s->is_xfs;
> +#endif
> +}
> +
>  /* XXX: use host sector size if necessary with:
>  #ifdef DIOCGSECTORSIZE
>          {
> @@ -735,6 +853,9 @@ static BlockDriver bdrv_file = {
>      .instance_size = sizeof(BDRVRawState),
>      .bdrv_probe = NULL, /* no probe for protocols */
>      .bdrv_file_open = raw_open,
> +    .bdrv_reopen_prepare = raw_reopen_prepare,
> +    .bdrv_reopen_commit = raw_reopen_commit,
> +    .bdrv_reopen_abort = raw_reopen_abort,
>      .bdrv_close = raw_close,
>      .bdrv_create = raw_create,
>      .bdrv_co_discard = raw_co_discard,
> 
>