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





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?



>  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.


>       /* 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


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