CF card and /dev filesystem entries

From: Brian Candler (B.Candler_at_pobox.com)
Date: 11/16/05

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    Date: Wed, 16 Nov 2005 10:12:00 +0000
To: freebsd-stable@freebsd.org

    Running FreeBSD 6.0 here.

    I have a USB-attached floppy/CF/SD combo reader. On powerup it is detected
    and I get /dev/da0 as the CF slot:

    da0 at umass-sim0 bus 0 target 0 lun 0
    da0: <OEI-USB CompactFlash 2.0> Removable Direct Access SCSI-0 device
    da0: 1.000MB/s transfers
    da0: Attempt to query device size failed: NOT READY, Medium not present
    da1 at umass-sim0 bus 0 target 0 lun 1
    da1: <OEI-USB SM/MS/SD 2.0> Removable Direct Access SCSI-0 device
    da1: 1.000MB/s transfers
    da1: Attempt to query device size failed: NOT READY, Medium not present

    However, when I insert a CF card with normal partioning I need /dev/da0s1,
    and this is not present in the /dev filesystem because the partition table
    has not been read.

    # mount -t msdos /dev/da0s1 /mnt/cf
    mount_msdosfs: /dev/da0s1: No such file or directory

    Just reading the first block is not sufficient:

    # dd if=/dev/da0 of=/dev/null count=1
    1+0 records in
    1+0 records out
    512 bytes transferred in 0.040984 secs (12493 bytes/sec)
    # mount -t msdos /dev/da0s1 /mnt/cf
    mount_msdosfs: /dev/da0s1: No such file or directory

    The only way I can see to *force* the superblock to be read is to attempt to
    mount the whole device as if it were unpartitioned. This is sufficient to
    cause the /dev/da0s1 entry to appear in the /dev filesystem.

    # mount /dev/da0 /mnt/cf
    mount: /dev/da0 on /mnt/cf: incorrect super block
    # mount -t msdos /dev/da0s1 /mnt/cf
    #

    At this point, everything works as expected.

    My question is: is there an easier or more direct way to cause the partition
    table of the CF card to be read and the /dev filesystem to update?

    Thanks,

    Brian Candler.
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