Re: [Qemu-devel] [PATCH v3 08/29] raw: Probe required direct I/O alignment

["Benoît Canet" <benoit.canet@irqsave.net>]

Le Friday 17 Jan 2014 à 15:14:58 (+0100), Kevin Wolf a écrit :
> From: Paolo Bonzini <pbonzini@redhat.com>
> 
> Add a bs->request_alignment field that contains the required
> offset/length alignment for I/O requests and fill it in the raw block
> drivers. Use ioctls if possible, else see what alignment it takes for
> O_DIRECT to succeed.
> 
> While at it, also expose the memory alignment requirements, which may be
> (and in practice are) different from the disk alignment requirements.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c                   |   3 ++
>  block/raw-posix.c         | 102 ++++++++++++++++++++++++++++++++++++++--------
>  block/raw-win32.c         |  41 +++++++++++++++++++
>  include/block/block_int.h |   3 ++
>  4 files changed, 132 insertions(+), 17 deletions(-)
> 
> diff --git a/block.c b/block.c
> index b738abe..25ae896 100644
> --- a/block.c
> +++ b/block.c
> @@ -813,6 +813,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
>  
>      bs->open_flags = flags;
>      bs->guest_block_size = 512;
> +    bs->request_alignment = 512;
>      bs->zero_beyond_eof = true;
>      open_flags = bdrv_open_flags(bs, flags);
>      bs->read_only = !(open_flags & BDRV_O_RDWR);
> @@ -881,6 +882,8 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
>      }
>  
>      bdrv_refresh_limits(bs);
> +    assert(bdrv_opt_mem_align(bs) != 0);
> +    assert(bs->request_alignment != 0);
>  
>  #ifndef _WIN32
>      if (bs->is_temporary) {
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 0676037..126a634 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -127,6 +127,8 @@ typedef struct BDRVRawState {
>      int fd;
>      int type;
>      int open_flags;
> +    size_t buf_align;
> +
>  #if defined(__linux__)
>      /* linux floppy specific */
>      int64_t fd_open_time;
> @@ -213,6 +215,76 @@ static int raw_normalize_devicepath(const char **filename)
>  }
>  #endif
>  
> +static void raw_probe_alignment(BlockDriverState *bs)
> +{
> +    BDRVRawState *s = bs->opaque;
> +    char *buf;
> +    unsigned int sector_size;
> +
> +    /* For /dev/sg devices the alignment is not really used.
> +       With buffered I/O, we don't have any restrictions. */
> +    if (bs->sg || !(s->open_flags & O_DIRECT)) {
> +        bs->request_alignment = 1;
> +        s->buf_align = 1;
> +        return;
> +    }
> +
> +    /* Try a few ioctls to get the right size */
> +    bs->request_alignment = 0;
> +    s->buf_align = 0;
> +
> +#ifdef BLKSSZGET
> +    if (ioctl(s->fd, BLKSSZGET, &sector_size) >= 0) {
> +        bs->request_alignment = sector_size;
> +    }
> +#endif
> +#ifdef DKIOCGETBLOCKSIZE
> +    if (ioctl(s->fd, DKIOCGETBLOCKSIZE, &sector_size) >= 0) {
> +        bs->request_alignment = sector_size;
> +    }
> +#endif
> +#ifdef DIOCGSECTORSIZE
> +    if (ioctl(s->fd, DIOCGSECTORSIZE, &sector_size) >= 0) {
> +        bs->request_alignment = sector_size;
> +    }
> +#endif
> +#ifdef CONFIG_XFS
> +    if (s->is_xfs) {
> +        struct dioattr da;
> +        if (xfsctl(NULL, s->fd, XFS_IOC_DIOINFO, &da) >= 0) {
> +            bs->request_alignment = da.d_miniosz;
> +            /* The kernel returns wrong information for d_mem */
> +            /* s->buf_align = da.d_mem; */
> +        }
> +    }
> +#endif
> +
> +    /* If we could not get the sizes so far, we can only guess them */
> +    if (!s->buf_align) {
> +        size_t align;
> +        buf = qemu_memalign(MAX_BLOCKSIZE, 2 * MAX_BLOCKSIZE);
> +        for (align = 512; align <= MAX_BLOCKSIZE; align <<= 1) {
> +            if (pread(s->fd, buf + align, MAX_BLOCKSIZE, 0) >= 0) {
> +                s->buf_align = align;
> +                break;
> +            }
> +        }
> +        qemu_vfree(buf);
> +    }
> +
> +    if (!bs->request_alignment) {
> +        size_t align;
> +        buf = qemu_memalign(s->buf_align, MAX_BLOCKSIZE);
> +        for (align = 512; align <= MAX_BLOCKSIZE; align <<= 1) {
> +            if (pread(s->fd, buf, align, 0) >= 0) {
> +                bs->request_alignment = align;
> +                break;
> +            }
> +        }
> +        qemu_vfree(buf);
> +    }
> +}
> +
>  static void raw_parse_flags(int bdrv_flags, int *open_flags)
>  {
>      assert(open_flags != NULL);
> @@ -463,7 +535,6 @@ static int raw_reopen_prepare(BDRVReopenState *state,
>      return ret;
>  }
>  
> -
>  static void raw_reopen_commit(BDRVReopenState *state)
>  {
>      BDRVRawReopenState *raw_s = state->opaque;
> @@ -499,23 +570,15 @@ static void raw_reopen_abort(BDRVReopenState *state)
>      state->opaque = NULL;
>  }
>  
> +static int raw_refresh_limits(BlockDriverState *bs)
> +{
> +    BDRVRawState *s = bs->opaque;
>  
> -/* XXX: use host sector size if necessary with:
> -#ifdef DIOCGSECTORSIZE
> -        {
> -            unsigned int sectorsize = 512;
> -            if (!ioctl(fd, DIOCGSECTORSIZE, &sectorsize) &&
> -                sectorsize > bufsize)
> -                bufsize = sectorsize;
> -        }
> -#endif
> -#ifdef CONFIG_COCOA
> -        uint32_t blockSize = 512;
> -        if ( !ioctl( fd, DKIOCGETBLOCKSIZE, &blockSize ) && blockSize > bufsize) {
> -            bufsize = blockSize;
> -        }
> -#endif
> -*/
> +    raw_probe_alignment(bs);
> +    bs->bl.opt_mem_alignment = s->buf_align;
> +
> +    return 0;
> +}
>  
>  static ssize_t handle_aiocb_ioctl(RawPosixAIOData *aiocb)
>  {
> @@ -1363,6 +1426,7 @@ static BlockDriver bdrv_file = {
>      .bdrv_aio_writev = raw_aio_writev,
>      .bdrv_aio_flush = raw_aio_flush,
>      .bdrv_aio_discard = raw_aio_discard,
> +    .bdrv_refresh_limits = raw_refresh_limits,
>  
>      .bdrv_truncate = raw_truncate,
>      .bdrv_getlength = raw_getlength,
> @@ -1740,6 +1804,7 @@ static BlockDriver bdrv_host_device = {
>      .bdrv_aio_writev	= raw_aio_writev,
>      .bdrv_aio_flush	= raw_aio_flush,
>      .bdrv_aio_discard   = hdev_aio_discard,
> +    .bdrv_refresh_limits = raw_refresh_limits,
>  
>      .bdrv_truncate      = raw_truncate,
>      .bdrv_getlength	= raw_getlength,
> @@ -1871,6 +1936,7 @@ static BlockDriver bdrv_host_floppy = {
>      .bdrv_aio_readv     = raw_aio_readv,
>      .bdrv_aio_writev    = raw_aio_writev,
>      .bdrv_aio_flush	= raw_aio_flush,
> +    .bdrv_refresh_limits = raw_refresh_limits,
>  
>      .bdrv_truncate      = raw_truncate,
>      .bdrv_getlength      = raw_getlength,
> @@ -1981,6 +2047,7 @@ static BlockDriver bdrv_host_cdrom = {
>      .bdrv_aio_readv     = raw_aio_readv,
>      .bdrv_aio_writev    = raw_aio_writev,
>      .bdrv_aio_flush	= raw_aio_flush,
> +    .bdrv_refresh_limits = raw_refresh_limits,
>  
>      .bdrv_truncate      = raw_truncate,
>      .bdrv_getlength      = raw_getlength,
> @@ -2110,6 +2177,7 @@ static BlockDriver bdrv_host_cdrom = {
>      .bdrv_aio_readv     = raw_aio_readv,
>      .bdrv_aio_writev    = raw_aio_writev,
>      .bdrv_aio_flush	= raw_aio_flush,
> +    .bdrv_refresh_limits = raw_refresh_limits,
>  
>      .bdrv_truncate      = raw_truncate,
>      .bdrv_getlength      = raw_getlength,
> diff --git a/block/raw-win32.c b/block/raw-win32.c
> index ce314fd..beb7f23 100644
> --- a/block/raw-win32.c
> +++ b/block/raw-win32.c
> @@ -202,6 +202,35 @@ static int set_sparse(int fd)
>  				 NULL, 0, NULL, 0, &returned, NULL);
>  }
>  
> +static void raw_probe_alignment(BlockDriverState *bs)
> +{
> +    BDRVRawState *s = bs->opaque;
> +    DWORD sectorsPerCluster, freeClusters, totalClusters, count;
> +    DISK_GEOMETRY_EX dg;
> +    BOOL status;
> +
> +    if (s->type == FTYPE_CD) {
> +        bs->request_alignment = 2048;
> +        return;
> +    }
> +    if (s->type == FTYPE_HARDDISK) {
> +        status = DeviceIoControl(s->hfile, IOCTL_DISK_GET_DRIVE_GEOMETRY_EX,
> +                                 NULL, 0, &dg, sizeof(dg), &count, NULL);
> +        if (status != 0) {
> +            bs->request_alignment = dg.Geometry.BytesPerSector;
> +            return;
> +        }
> +        /* try GetDiskFreeSpace too */
> +    }
> +
> +    if (s->drive_path[0]) {
> +        GetDiskFreeSpace(s->drive_path, &sectorsPerCluster,
> +                         &dg.Geometry.BytesPerSector,
> +                         &freeClusters, &totalClusters);
> +        bs->request_alignment = dg.Geometry.BytesPerSector;
> +    }
> +}
> +
>  static void raw_parse_flags(int flags, int *access_flags, DWORD *overlapped)
>  {
>      assert(access_flags != NULL);
> @@ -269,6 +298,17 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
>          }
>      }
>  
> +    if (filename[0] && filename[1] == ':') {
> +        snprintf(s->drive_path, sizeof(s->drive_path), "%c:\\", filename[0]);
> +    } else if (filename[0] == '\\' && filename[1] == '\\') {
> +        s->drive_path[0] = 0;
> +    } else {
> +        /* Relative path.  */
> +        char buf[MAX_PATH];
> +        GetCurrentDirectory(MAX_PATH, buf);
> +        snprintf(s->drive_path, sizeof(s->drive_path), "%c:\\", buf[0]);
> +    }
> +
This is not really alignment related.
Does this really belong to this patch ?

Best regards

Benoît
>      s->hfile = CreateFile(filename, access_flags,
>                            FILE_SHARE_READ, NULL,
>                            OPEN_EXISTING, overlapped, NULL);
> @@ -293,6 +333,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
>          s->aio = aio;
>      }
>  
> +    raw_probe_alignment(bs);
>      ret = 0;
>  fail:
>      qemu_opts_del(opts);
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 36c068f..fb1d355 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -319,6 +319,9 @@ struct BlockDriverState {
>      /* Whether produces zeros when read beyond eof */
>      bool zero_beyond_eof;
>  
> +    /* Alignment requirement for offset/length of I/O requests */
> +    unsigned int request_alignment;
> +
>      /* the block size for which the guest device expects atomicity */
>      int guest_block_size;
>  
> -- 
> 1.8.1.4
> 
>