On Tue, 2015-04-28 at 14:25 -0400, Dan Williams wrote:
> Block devices from an nd bus, in addition to accepting "struct bio"
> based requests, also have the capability to perform byte-aligned
> accesses. By default only the bio/block interface is used. However, if
> another driver can make effective use of the byte-aligned capability it
> can claim/disable the block interface and use the byte-aligned "nd_io"
> interface.
>
> The BTT driver is the intended first consumer of this mechanism to allow
> layering atomic sector update guarantees on top of nd_io capable
> nd-bus-block-devices.
:
> +static int nd_btt_autodetect(struct nd_bus *nd_bus, struct nd_io *ndio,
> + struct block_device *bdev)
> +{
> + char name[BDEVNAME_SIZE];
> + struct nd_btt *nd_btt;
> + struct btt_sb *btt_sb;
> + u64 offset, checksum;
> + u32 lbasize;
> + u8 *uuid;
> + int rc;
> +
> + btt_sb = kzalloc(sizeof(*btt_sb), GFP_KERNEL);
> + if (!btt_sb)
> + return -ENODEV;
> +
> + offset = nd_partition_offset(bdev);
> + rc = ndio->rw_bytes(ndio, btt_sb, offset + SZ_4K, sizeof(*btt_sb),
> READ);
> + if (rc)
> + goto out_free_sb;
> +
> + if (get_capacity(bdev->bd_disk) < SZ_16M / 512)
> + goto out_free_sb;
> +
> + if (memcmp(btt_sb->signature, BTT_SIG, BTT_SIG_LEN) != 0)
> + goto out_free_sb;
> +
> + checksum = le64_to_cpu(btt_sb->checksum);
> + btt_sb->checksum = 0;
> + if (checksum != nd_btt_sb_checksum(btt_sb))
> + goto out_free_sb;
> + btt_sb->checksum = cpu_to_le64(checksum);
> +
> + uuid = kmemdup(btt_sb->uuid, 16, GFP_KERNEL);
> + if (!uuid)
> + goto out_free_sb;
> +
> + lbasize = le32_to_cpu(btt_sb->external_lbasize);
> + nd_btt = __nd_btt_create(nd_bus, lbasize, uuid);
When BTT is first set up, user binds a seed "btt0" to a block device,
such as /dev/pmem0. It then creates /dev/nd0 bound to /dev/pmem0.
After a reboot, nd_btt_autodetect() detects the BTT setup and creates a
new "btt1" since it is called after a seed "btt0" is created.
Therefore, it creates /dev/nd1 bound to /dev/pmem0 this time.
Is this how it is intended to work, i.e. "btt0" as the default seed btt?
While user should not rely on the name of /dev/nd%d, I thought this
device name change was confusing...
Thanks,
-Toshi
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