Re: [Qemu-devel] [v7 Patch 5/5]Qemu: New struct 'BDRVReopenState' for image files reopen

[Kevin Wolf <kwolf@redhat.com>]

Am 11.10.2011 05:11, schrieb Supriya Kannery:
> Struct BDRVReopenState introduced for handling reopen state of images. 
> This can be  extended by each of the block drivers to reopen respective
> image files. Implementation for raw-posix is done here.
> 
> Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>

Maybe it would make sense to split this into two patches, one for the
block.c infrastructure and another one for adding the callbacks in drivers.

> ---
>  block.c           |   46 ++++++++++++++++++++++++++++++++--------
>  block/raw-posix.c |   62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  block_int.h       |   15 +++++++++++++
>  3 files changed, 114 insertions(+), 9 deletions(-)
> 
> Index: qemu/block/raw-posix.c
> ===================================================================
> --- qemu.orig/block/raw-posix.c
> +++ qemu/block/raw-posix.c
> @@ -279,6 +279,66 @@ static int raw_open(BlockDriverState *bs
>      return raw_open_common(bs, filename, flags, 0);
>  }
>  
> +static int raw_reopen_prepare(BlockDriverState *bs, BDRVReopenState **rs,
> +                              int flags)
> +{
> +    BDRVReopenState *raw_rs = g_malloc0(sizeof(BDRVReopenState));
> +    BDRVRawState *s = bs->opaque;
> +
> +    raw_rs->bs = bs;
> +    raw_rs->reopen_flags = flags;
> +    raw_rs->reopen_fd = -1;
> +
> +    /* If only O_DIRECT to be toggled, use fcntl */
> +    if (!((bs->open_flags & ~BDRV_O_NOCACHE) ^
> +            (flags & ~BDRV_O_NOCACHE))) {
> +        raw_rs->reopen_fd = dup(s->fd);
> +        if (raw_rs->reopen_fd <= 0) {
> +            return -1;

This leaks raw_rs.

> +        }
> +    }
> +
> +    /* TBD: Handle O_DSYNC and other flags */
> +    *rs = raw_rs;
> +    return 0;
> +}
> +
> +static int raw_reopen_commit(BDRVReopenState *rs)

bdrv_reopen_commit must never fail. Any error that can happen must
already be handled in bdrv_reopen_prepare.

The commit function should really only do s->fd = rs->reopen_fd (besides
cleanup), everything else should already be prepared.

> +{
> +    BlockDriverState *bs = rs->bs;
> +    BDRVRawState *s = bs->opaque;
> +
> +    if (!rs->reopen_fd) {
> +        return -1;
> +    }
> +
> +    int ret = fcntl_setfl(rs->reopen_fd, rs->reopen_flags);

reopen_flags is BDRV_O_*, not O_*, so it needs to be translated.

> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    /* Set new flags, so replace old fd with new one */
> +    close(s->fd);
> +    s->fd = rs->reopen_fd;
> +    s->open_flags = bs->open_flags = rs->reopen_flags;
> +    g_free(rs);
> +    rs = NULL;

Setting to NULL has no effect, rs isn't read afterwards.

> +
> +    return 0;
> +}
> +
> +static int raw_reopen_abort(BDRVReopenState *rs)

This must not fail either, so it can be void, too.

> +{
> +    if (rs->reopen_fd != -1) {
> +        close(rs->reopen_fd);
> +        rs->reopen_fd = -1;
> +        rs->reopen_flags = 0;
> +    }
> +    g_free(rs);
> +    rs = NULL;
> +    return 0;
> +}
> +
>  /* XXX: use host sector size if necessary with:
>  #ifdef DIOCGSECTORSIZE
>          {
> @@ -896,6 +956,9 @@ 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_read = raw_read,
>      .bdrv_write = raw_write,
>      .bdrv_close = raw_close,
> @@ -1166,6 +1229,10 @@ static BlockDriver bdrv_host_device = {
>      .instance_size      = sizeof(BDRVRawState),
>      .bdrv_probe_device  = hdev_probe_device,
>      .bdrv_file_open     = hdev_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        = hdev_create,
>      .create_options     = raw_create_options,
> Index: qemu/block.c
> ===================================================================
> --- qemu.orig/block.c
> +++ qemu/block.c
> @@ -706,6 +706,7 @@ int bdrv_reopen(BlockDriverState *bs, in
>  {
>      BlockDriver *drv = bs->drv;
>      int ret = 0, open_flags;
> +    BDRVReopenState *rs;
>  
>      /* Quiesce IO for the given block device */
>      qemu_aio_flush();
> @@ -713,20 +714,48 @@ int bdrv_reopen(BlockDriverState *bs, in
>          qerror_report(QERR_DATA_SYNC_FAILED, bs->device_name);
>          return ret;
>      }
> -    open_flags = bs->open_flags;
> -    bdrv_close(bs);
>  
> -    ret = bdrv_open(bs, bs->filename, bdrv_flags, drv);
> -    if (ret < 0) {
> -        /* Reopen failed. Try to open with original flags */
> -        qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
> -        ret = bdrv_open(bs, bs->filename, open_flags, drv);
> +    /* Use driver specific reopen() if available */
> +    if (drv->bdrv_reopen_prepare) {
> +        ret = drv->bdrv_reopen_prepare(bs, &rs, bdrv_flags);
>          if (ret < 0) {
> -            /* Reopen failed with orig and modified flags */
> -            abort();
> +            goto fail;
>          }
> -    }
> +        if (drv->bdrv_reopen_commit) {
> +            ret = drv->bdrv_reopen_commit(rs);
> +            if (ret < 0) {
> +                goto fail;
> +            }
> +            return 0;
> +        }

Pull the return 0; out one level. It would be really strange if we
turned a successful prepare into reopen_abort just because the driver
doesn't need a commit function.

(The other consistent way would be to require that if a driver
implements one reopen function, it has to implement all three of them.
I'm fine either way.)

> +fail:
> +        if (drv->bdrv_reopen_abort) {
> +            ret = drv->bdrv_reopen_abort(rs);
> +            qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
> +            return ret;
> +        }
> +
> +    } else {
> +
> +        /* Use reopen procedure common for all drivers */
> +        open_flags = bs->open_flags;
> +        bdrv_close(bs);
>  
> +        ret = bdrv_open(bs, bs->filename, bdrv_flags, drv);
> +        if (ret < 0) {
> +            /*
> +             * Reopen failed. Try to open with original flags
> +            */
> +            qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
> +            ret = bdrv_open(bs, bs->filename, open_flags, drv);
> +            if (ret < 0) {
> +                /*
> +                 * Reopen with orig and modified flags failed
> +                 */
> +                abort();

Make this bs->drv = NULL, so that trying to access to image will fail,
but at least not the whole VM crashes.

> +            }
> +        }
> +    }
>      return ret;
>  }
>  
> Index: qemu/block_int.h
> ===================================================================
> --- qemu.orig/block_int.h
> +++ qemu/block_int.h
> @@ -55,6 +55,13 @@ struct BlockDriver {
>      int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
>      int (*bdrv_probe_device)(const char *filename);
>      int (*bdrv_open)(BlockDriverState *bs, int flags);
> +
> +    /* For handling image reopen for split or non-split files */
> +    int (*bdrv_reopen_prepare)(BlockDriverState *bs, BDRVReopenState **rs,
> +          int flags);
> +    int (*bdrv_reopen_commit)(BDRVReopenState *rs);
> +    int (*bdrv_reopen_abort)(BDRVReopenState *rs);
> +
>      int (*bdrv_file_open)(BlockDriverState *bs, const char *filename, int flags);
>      int (*bdrv_read)(BlockDriverState *bs, int64_t sector_num,
>                       uint8_t *buf, int nb_sectors);
> @@ -207,6 +214,14 @@ struct BlockDriverState {
>      void *private;
>  };
>  
> +struct BDRVReopenState {
> +    BlockDriverState *bs;
> +    int reopen_flags;
> +
> +    /* For raw-posix */
> +    int reopen_fd;
> +};
> +
>  struct BlockDriverAIOCB {
>      AIOPool *pool;
>      BlockDriverState *bs;
> Index: qemu/qemu-common.h
> ===================================================================
> --- qemu.orig/qemu-common.h
> +++ qemu/qemu-common.h
> @@ -228,6 +228,7 @@ typedef struct NICInfo NICInfo;
>  typedef struct HCIInfo HCIInfo;
>  typedef struct AudioState AudioState;
>  typedef struct BlockDriverState BlockDriverState;
> +typedef struct BDRVReopenState BDRVReopenState;
>  typedef struct DriveInfo DriveInfo;
>  typedef struct DisplayState DisplayState;
>  typedef struct DisplayChangeListener DisplayChangeListener;
> Index: qemu/block/raw.c
> ===================================================================
> --- qemu.orig/block/raw.c
> +++ qemu/block/raw.c
> @@ -9,6 +9,15 @@ static int raw_open(BlockDriverState *bs
>      return 0;
>  }
>  
> +static int raw_reopen(BlockDriverState *bs, BDRVReopenState **prs, int flags)
> +{
> +    int ret = bdrv_reopen(bs->file, flags);
> +    if (!ret) {
> +        bs->open_flags = bs->file->open_flags;
> +    }
> +    return ret;
> +}
> +
>  static int raw_read(BlockDriverState *bs, int64_t sector_num,
>                      uint8_t *buf, int nb_sectors)
>  {
> @@ -128,6 +137,8 @@ static BlockDriver bdrv_raw = {
>      .instance_size      = 1,
>  
>      .bdrv_open          = raw_open,
> +    .bdrv_reopen_prepare
> +                        = raw_reopen,
>      .bdrv_close         = raw_close,
>      .bdrv_read          = raw_read,
>      .bdrv_write         = raw_write,

I think raw must pass through all three functions. Otherwise it could
happen that we need to abort, but the image has already been reopened.

Kevin