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Re: [libvirt] [Qemu-devel] [PATCH v2] Add support for fd: protocol





On 06/18/2011 04:50 PM, Blue Swirl wrote:
On Thu, Jun 16, 2011 at 5:48 PM, Corey Bryant<bryntcor us ibm com>  wrote:


On 06/15/2011 03:12 PM, Blue Swirl wrote:

On Tue, Jun 14, 2011 at 4:31 PM, Corey Bryant<bryntcor us ibm com>    wrote:

  sVirt provides SELinux MAC isolation for Qemu guest processes and
their
  corresponding resources (image files). sVirt provides this support
  by labeling guests and resources with security labels that are stored
  in file system extended attributes. Some file systems, such as NFS, do
  not support the extended attribute security namespace, which is needed
  for image file isolation when using the sVirt SELinux security driver
  in libvirt.

  The proposed solution entails a combination of Qemu, libvirt, and
  SELinux patches that work together to isolate multiple guests' images
  when they're stored in the same NFS mount. This results in an
  environment where sVirt isolation and NFS image file isolation can
both
  be provided.

  This patch contains the Qemu code to support this solution. I would
  like to solicit input from the libvirt community prior to starting
  the libvirt patch.

  Currently, Qemu opens an image file in addition to performing the
  necessary read and write operations. The proposed solution will move
  the open out of Qemu and into libvirt. Once libvirt opens an image
  file for the guest, it will pass the file descriptor to Qemu via a
  new fd: protocol.

  If the image file resides in an NFS mount, the following SELinux
policy
  changes will provide image isolation:

    - A new SELinux boolean is created (e.g. virt_read_write_nfs) to
      allow Qemu (svirt_t) to only have SELinux read and write
      permissions on nfs_t files

    - Qemu (svirt_t) also gets SELinux use permissions on libvirt
      (virtd_t) file descriptors

  Following is a sample invocation of Qemu using the fd: protocol on
  the command line:

      qemu -drive file=fd:4,format=qcow2

  The fd: protocol is also supported by the drive_add monitor command.
  This requires that the specified file descriptor is passed to the
  monitor alongside a prior getfd monitor command.

  There are some additional features provided by certain image types
  where Qemu reopens the image file. All of these scenarios will be
  unsupported for the fd: protocol, at least for this patch:

    - The -snapshot command line option
    - The savevm monitor command
    - The snapshot_blkdev monitor command
    - Starting Qemu with a backing file

There's also native CDROM device. Did you consider adding an explicit
reopen method to block layer?

Thanks. Yes it looks like I overlooked CDROM reopens.

I'm not sure that I'm clear on the purpose of the reopen function. Would the
goal be to funnel all block layer reopens through a single function,
enabling potential future support where a privileged layer of Qemu, or
libvirt, performs the open?

Eventually yes, but I think it would help also now by moving the
checks to a single place. It's a bit orthogonal to this patch though.


This would definitely simplify things, especially when reopen support is added. I'm going to defer this until then.

  The thought is that this support can be added in the future, but is
  not required for the initial fd: support.

  This patch was tested with the following formats: raw, cow, qcow,
  qcow2, qed, and vmdk, using the fd: protocol from the command line
  and the monitor. Tests were also run to verify existing file name
  support and qemu-img were not regressed. Non-valid file descriptors,
  fd: without format, snapshot and backing files were also tested.

  Signed-off-by: Corey Bryant<coreyb linux vnet ibm com>
  ---
    block.c           |   16 ++++++++++
    block.h           |    1 +
    block/cow.c       |    5 +++
    block/qcow.c      |    5 +++
    block/qcow2.c     |    5 +++
    block/qed.c       |    4 ++
    block/raw-posix.c |   81
+++++++++++++++++++++++++++++++++++++++++++++++------
    block/vmdk.c      |    5 +++
    block_int.h       |    1 +
    blockdev.c        |   10 ++++++
    monitor.c         |    5 +++
    monitor.h         |    1 +
    qemu-options.hx   |    8 +++--
    qemu-tool.c       |    5 +++
    14 files changed, 140 insertions(+), 12 deletions(-)

  diff --git a/block.c b/block.c
  index 24a25d5..500db84 100644
  --- a/block.c
  +++ b/block.c
  @@ -536,6 +536,10 @@ int bdrv_open(BlockDriverState *bs, const char
*filename, int flags,
           char tmp_filename[PATH_MAX];
           char backing_filename[PATH_MAX];

  +        if (bdrv_is_fd_protocol(bs)) {
  +            return -ENOTSUP;
  +        }
  +
           /* if snapshot, we create a temporary backing file and open
it
              instead of opening 'filename' directly */

  @@ -585,6 +589,10 @@ int bdrv_open(BlockDriverState *bs, const char
*filename, int flags,

       /* Find the right image format driver */
       if (!drv) {
  +        /* format must be specified for fd: protocol */
  +        if (bdrv_is_fd_protocol(bs)) {
  +            return -ENOTSUP;
  +        }
           ret = find_image_format(filename,&drv);
       }

  @@ -1460,6 +1468,11 @@ int bdrv_enable_write_cache(BlockDriverState
*bs)
       return bs->enable_write_cache;
    }

  +int bdrv_is_fd_protocol(BlockDriverState *bs)
  +{
  +    return bs->fd_protocol;
  +}
  +
    /* XXX: no longer used */
    void bdrv_set_change_cb(BlockDriverState *bs,
                           void (*change_cb)(void *opaque, int reason),
  @@ -1964,6 +1977,9 @@ int bdrv_snapshot_create(BlockDriverState *bs,
       BlockDriver *drv = bs->drv;
       if (!drv)
           return -ENOMEDIUM;
  +    if (bdrv_is_fd_protocol(bs)) {
  +        return -ENOTSUP;
  +    }
       if (drv->bdrv_snapshot_create)
           return drv->bdrv_snapshot_create(bs, sn_info);
       if (bs->file)
  diff --git a/block.h b/block.h
  index da7d39c..dd46d52 100644
  --- a/block.h
  +++ b/block.h
  @@ -182,6 +182,7 @@ int bdrv_is_removable(BlockDriverState *bs);
    int bdrv_is_read_only(BlockDriverState *bs);
    int bdrv_is_sg(BlockDriverState *bs);
    int bdrv_enable_write_cache(BlockDriverState *bs);
  +int bdrv_is_fd_protocol(BlockDriverState *bs);
    int bdrv_is_inserted(BlockDriverState *bs);
    int bdrv_media_changed(BlockDriverState *bs);
    int bdrv_is_locked(BlockDriverState *bs);
  diff --git a/block/cow.c b/block/cow.c
  index 4cf543c..e17f8e7 100644
  --- a/block/cow.c
  +++ b/block/cow.c
  @@ -82,6 +82,11 @@ static int cow_open(BlockDriverState *bs, int
flags)
       pstrcpy(bs->backing_file, sizeof(bs->backing_file),
               cow_header.backing_file);

  +    if (bs->backing_file[0] != '\0'&&    bdrv_is_fd_protocol(bs)) {
  +        /* backing file currently not supported by fd: protocol */
  +        goto fail;
  +    }
  +
       bitmap_size = ((bs->total_sectors + 7)>>    3) +
sizeof(cow_header);
       s->cow_sectors_offset = (bitmap_size + 511)&    ~511;
       return 0;
  diff --git a/block/qcow.c b/block/qcow.c
  index a26c886..1e46bdb 100644
  --- a/block/qcow.c
  +++ b/block/qcow.c
  @@ -157,6 +157,11 @@ static int qcow_open(BlockDriverState *bs, int
flags)
           if (bdrv_pread(bs->file, header.backing_file_offset,
bs->backing_file, len) != len)
               goto fail;
           bs->backing_file[len] = '\0';
  +
  +        if (bs->backing_file[0] != '\0'&&    bdrv_is_fd_protocol(bs)) {
  +            /* backing file currently not supported by fd: protocol
*/
  +            goto fail;
  +        }
       }
       return 0;

  diff --git a/block/qcow2.c b/block/qcow2.c
  index 8451ded..8b9c160 100644
  --- a/block/qcow2.c
  +++ b/block/qcow2.c
  @@ -270,6 +270,11 @@ static int qcow2_open(BlockDriverState *bs, int
flags)
               goto fail;
           }
           bs->backing_file[len] = '\0';
  +
  +        if (bs->backing_file[0] != '\0'&&    bdrv_is_fd_protocol(bs)) {
  +            ret = -ENOTSUP;
  +            goto fail;
  +        }
       }
       if (qcow2_read_snapshots(bs)<    0) {
           ret = -EINVAL;
  diff --git a/block/qed.c b/block/qed.c
  index 3970379..5028897 100644
  --- a/block/qed.c
  +++ b/block/qed.c
  @@ -446,6 +446,10 @@ static int bdrv_qed_open(BlockDriverState *bs,
int flags)
               return ret;
           }

  +        if (bs->backing_file[0] != '\0'&&    bdrv_is_fd_protocol(bs)) {
  +            return -ENOTSUP;
  +        }
  +
           if (s->header.features&    QED_F_BACKING_FORMAT_NO_PROBE) {
               pstrcpy(bs->backing_format, sizeof(bs->backing_format),
"raw");
           }
  diff --git a/block/raw-posix.c b/block/raw-posix.c
  index 4cd7d7a..c72de3d 100644
  --- a/block/raw-posix.c
  +++ b/block/raw-posix.c
  @@ -28,6 +28,7 @@
    #include "block_int.h"
    #include "module.h"
    #include "block/raw-posix-aio.h"
  +#include "monitor.h"

    #ifdef CONFIG_COCOA
    #include<paths.h>
  @@ -183,7 +184,8 @@ static int raw_open_common(BlockDriverState *bs,
const char *filename,
                              int bdrv_flags, int open_flags)
    {
       BDRVRawState *s = bs->opaque;
  -    int fd, ret;
  +    int fd = -1;
  +    int ret;

       ret = raw_normalize_devicepath(&filename);
       if (ret != 0) {
  @@ -205,15 +207,17 @@ static int raw_open_common(BlockDriverState *bs,
const char *filename,
       if (!(bdrv_flags&    BDRV_O_CACHE_WB))
           s->open_flags |= O_DSYNC;

  -    s->fd = -1;
  -    fd = qemu_open(filename, s->open_flags, 0644);
  -    if (fd<    0) {
  -        ret = -errno;
  -        if (ret == -EROFS)
  -            ret = -EACCES;
  -        return ret;
  +    if (s->fd == -1) {
  +        fd = qemu_open(filename, s->open_flags, 0644);
  +        if (fd<    0) {
  +            ret = -errno;
  +            if (ret == -EROFS) {
  +                ret = -EACCES;
  +            }
  +            return ret;
  +        }
  +        s->fd = fd;
       }
  -    s->fd = fd;
       s->aligned_buf = NULL;

       if ((bdrv_flags&    BDRV_O_NOCACHE)) {
  @@ -270,6 +274,7 @@ static int raw_open(BlockDriverState *bs, const
char *filename, int flags)
    {
       BDRVRawState *s = bs->opaque;

  +    s->fd = -1;
       s->type = FTYPE_FILE;
       return raw_open_common(bs, filename, flags, 0);
    }
  @@ -890,6 +895,60 @@ static BlockDriver bdrv_file = {
       .create_options = raw_create_options,
    };

  +static int raw_open_fd(BlockDriverState *bs, const char *filename,
int flags)
  +{
  +    BDRVRawState *s = bs->opaque;
  +    const char *fd_str;
  +    int fd;
  +
  +    /* extract the file descriptor - fail if it's not fd: */
  +    if (!strstart(filename, "fd:",&fd_str)) {
  +        return -EINVAL;
  +    }
  +
  +    if (!qemu_isdigit(fd_str[0])) {
  +        /* get fd from monitor */
  +        fd = qemu_get_fd(fd_str);
  +        if (fd == -1) {
  +            return -EBADF;
  +        }
  +    } else {
  +        char *endptr = NULL;
  +
  +        fd = strtol(fd_str,&endptr, 10);
  +        if (*endptr || (fd == 0&&    fd_str == endptr)) {
  +            return -EBADF;
  +        }
  +    }
  +
  +    s->fd = fd;
  +    s->type = FTYPE_FILE;
  +
  +    return raw_open_common(bs, filename, flags, 0);
  +}
  +
  +static BlockDriver bdrv_file_fd = {
  +    .format_name = "file",
  +    .protocol_name = "fd",
  +    .instance_size = sizeof(BDRVRawState),
  +    .bdrv_probe = NULL, /* no probe for protocols */
  +    .bdrv_file_open = raw_open_fd,
  +    .bdrv_read = raw_read,
  +    .bdrv_write = raw_write,
  +    .bdrv_close = raw_close,
  +    .bdrv_flush = raw_flush,
  +    .bdrv_discard = raw_discard,
  +
  +    .bdrv_aio_readv = raw_aio_readv,
  +    .bdrv_aio_writev = raw_aio_writev,
  +    .bdrv_aio_flush = raw_aio_flush,
  +
  +    .bdrv_truncate = raw_truncate,
  +    .bdrv_getlength = raw_getlength,
  +
  +    .create_options = raw_create_options,
  +};
  +
    /***********************************************/
    /* host device */

  @@ -998,6 +1057,7 @@ static int hdev_open(BlockDriverState *bs, const
char *filename, int flags)
       }
    #endif

  +    s->fd = -1;
       s->type = FTYPE_FILE;
    #if defined(__linux__)
       {
  @@ -1168,6 +1228,7 @@ static int floppy_open(BlockDriverState *bs,
const char *filename, int flags)
       BDRVRawState *s = bs->opaque;
       int ret;

  +    s->fd = -1;
       s->type = FTYPE_FD;

       /* open will not fail even if no floppy is inserted, so add
O_NONBLOCK */
  @@ -1280,6 +1341,7 @@ static int cdrom_open(BlockDriverState *bs,
const char *filename, int flags)
    {
       BDRVRawState *s = bs->opaque;

  +    s->fd = -1;
       s->type = FTYPE_CD;

       /* open will not fail even if no CD is inserted, so add
O_NONBLOCK */
  @@ -1503,6 +1565,7 @@ static void bdrv_file_init(void)
        * Register all the drivers.  Note that order is important, the
driver
        * registered last will get probed first.
        */
  +    bdrv_register(&bdrv_file_fd);
       bdrv_register(&bdrv_file);
       bdrv_register(&bdrv_host_device);
    #ifdef __linux__
  diff --git a/block/vmdk.c b/block/vmdk.c
  index 922b23d..2ea808e 100644
  --- a/block/vmdk.c
  +++ b/block/vmdk.c
  @@ -353,6 +353,11 @@ static int vmdk_parent_open(BlockDriverState *bs)
               return -1;

           pstrcpy(bs->backing_file, end_name - p_name + 1, p_name);
  +
  +        if (bs->backing_file[0] != '\0'&&    bdrv_is_fd_protocol(bs)) {
  +            /* backing file currently not supported by fd: protocol
*/
  +            return -1;
  +        }
       }

       return 0;
  diff --git a/block_int.h b/block_int.h
  index fa91337..a305ee2 100644
  --- a/block_int.h
  +++ b/block_int.h
  @@ -152,6 +152,7 @@ struct BlockDriverState {
       int encrypted; /* if true, the media is encrypted */
       int valid_key; /* if true, a valid encryption key has been set */
       int sg;        /* if true, the device is a /dev/sg* */
  +    int fd_protocol; /* if true, the fd: protocol was specified */

bool?

I was following suit here, but I agree that bool would be better.  Or
better, these could all be reduced to bit flags.  My thought is that I'll
stick with following suit here though.

OK, better convert all at once with a separate patch.


Ok

       /* event callback when inserting/removing */
       void (*change_cb)(void *opaque, int reason);
       void *change_opaque;
  diff --git a/blockdev.c b/blockdev.c
  index e81e0ab..a536c20 100644
  --- a/blockdev.c
  +++ b/blockdev.c
  @@ -546,6 +546,10 @@ DriveInfo *drive_init(QemuOpts *opts, int
default_to_scsi)

       bdrv_flags |= ro ? 0 : BDRV_O_RDWR;

  +    if (strncmp(file, "fd:", 3) == 0) {
  +        dinfo->bdrv->fd_protocol = 1;
  +    }
  +
       ret = bdrv_open(dinfo->bdrv, file, bdrv_flags, drv);
       if (ret<    0) {
           error_report("could not open disk image %s: %s",
  @@ -606,6 +610,12 @@ int do_snapshot_blkdev(Monitor *mon, const QDict
*qdict, QObject **ret_data)
           goto out;
       }

  +    if (bdrv_is_fd_protocol(bs)) {
  +        qerror_report(QERR_UNSUPPORTED);
  +        ret = -1;
  +        goto out;
  +    }
  +
       pstrcpy(old_filename, sizeof(old_filename), bs->filename);

       old_drv = bs->drv;
  diff --git a/monitor.c b/monitor.c
  index 59a3e76..ea60be2 100644
  --- a/monitor.c
  +++ b/monitor.c
  @@ -2832,6 +2832,11 @@ int monitor_get_fd(Monitor *mon, const char
*fdname)
       return -1;
    }

  +int qemu_get_fd(const char *fdname)
  +{
  +    return cur_mon ? monitor_get_fd(cur_mon, fdname) : -1;
  +}
  +
    static const mon_cmd_t mon_cmds[] = {
    #include "hmp-commands.h"
       { NULL, NULL, },
  diff --git a/monitor.h b/monitor.h
  index 4f2d328..de5b987 100644
  --- a/monitor.h
  +++ b/monitor.h
  @@ -51,6 +51,7 @@ int monitor_read_bdrv_key_start(Monitor *mon,
BlockDriverState *bs,
                                   void *opaque);

    int monitor_get_fd(Monitor *mon, const char *fdname);
  +int qemu_get_fd(const char *fdname);

    void monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
       GCC_FMT_ATTR(2, 0);
  diff --git a/qemu-options.hx b/qemu-options.hx
  index 1d5ad8b..f9b66f4 100644
  --- a/qemu-options.hx
  +++ b/qemu-options.hx
  @@ -116,7 +116,7 @@ using @file{/dev/cdrom} as filename
(@pxref{host_drives}).
    ETEXI

    DEF("drive", HAS_ARG, QEMU_OPTION_drive,
  -    "-drive
[file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n"
  +    "-drive
[file=[fd:]file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n"
       "       [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n"
       "       [,cache=writethrough|writeback|none|unsafe][,format=f]\n"
       "       [,serial=s][,addr=A][,id=name][,aio=threads|native]\n"
  @@ -129,10 +129,12 @@ STEXI
    Define a new drive. Valid options are:

    @table @option
  - item file= var{file}
  + item file=[fd:] var{file}
    This option defines which disk image (@pxref{disk_images}) to use
with
    this drive. If the filename contains comma, you must double it
  -(for instance, "file=my,,file" to use file "my,file").
  +(for instance, "file=my,,file" to use file "my,file").
@option{fd:} var{file}
  +specifies the file descriptor of an already open disk image.
+ option{format=}@var{format} is required by @option{fd:} var{file} @item if= var{interface}
    This option defines on which type on interface the drive is
connected.
    Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio.
  diff --git a/qemu-tool.c b/qemu-tool.c
  index 41e5c41..8fe6b8c 100644
  --- a/qemu-tool.c
  +++ b/qemu-tool.c
  @@ -96,3 +96,8 @@ int64_t qemu_get_clock_ns(QEMUClock *clock)
    {
       return 0;
    }
  +
  +int qemu_get_fd(const char *fdname)
  +{
  +    return -1;
  +}
  --
  1.7.1





Regards,
Corey Bryant


--
Regards,
Corey Bryant
IBM Linux Technology Center - Security
845-435-8732 (T/L: 295-8732)


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