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

[Kevin Wolf <kwolf@redhat.com>]

Am 21.01.2014 um 14:03 hat Benoît Canet geschrieben:
> 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 ?

raw_probe_alignment() needs the path, so s->drive_path must now be
initialised for all images. Without this change it is only set in
hdev_open(), i.e. for win32 host_device backends.

Kevin