Re: [Qemu-devel] [RFC Patch 5/7]Qemu: raw-posix image file reopen

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On 01/31/2012 09:07 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<supriyak@linux.vnet.ibm.com>
>
> 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);
> +}
> +
>   static int coroutine_fn raw_co_readv(BlockDriverState *bs, int64_t sector_num,
>                                        int nb_sectors, QEMUIOVector *qiov)
>   {
> @@ -109,6 +125,10 @@ 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
> @@ -136,6 +136,11 @@ 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);
>
> @@ -279,6 +284,71 @@ 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));
> +    memcpy(raw_rs->stash_s, s, sizeof(BDRVRawState));
> +    s->fd = dup(raw_rs->stash_s->fd);
> +
> +    *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;
> +        }
> +        printf("O_DIRECT flag\n");
> +        ret = fcntl_setfl(s->fd, s->open_flags);

raw-posix.c:raw_aio_submit() does some extra alignment work if 
s->aligned_buf was set due to the image being opened O_DIRECT initially, 
not sure what the impact is but probably want to clean that up here.

> +    } else {
> +
> +        printf("close and open with new flags\n");
> +        /* close and reopen using new flags */
> +        bs->drv->bdrv_close(bs);
> +        ret = bs->drv->bdrv_file_open(bs, bs->filename, flags);
> +    }
> +    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);
> +    }
> +    memcpy(s, raw_rs->stash_s, sizeof(BDRVRawState));
> +    g_free(raw_rs->stash_s);
> +    g_free(raw_rs);
> +}
> +
>   /* XXX: use host sector size if necessary with:
>   #ifdef DIOCGSECTORSIZE
>           {
> @@ -631,6 +701,9 @@ 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,
>
>