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    SubjectRe: [PATCH] scsi/sd: Fix size output in MB
    On 30/08/08 18:45, Matthew Wilcox wrote:
    > On Sat, Aug 30, 2008 at 12:24:50PM -0500, James Bottomley wrote:
    >> No, this is wrong. By mandated standards the manufacturers are allowed
    >> to calculate MB by dividing by 10^6. This is a fiddle to allow them to
    >> make their drives look slightly bigger. However, we want the printed
    >> information to match that written on the drive, so in this printk, we
    >> use the manufacturer standard for calculation (and then do everything
    >> else in bytes so we don't have to bother with it ever again).

    It's unlikely to match what's on the drive, "1000204886016" isn't 1TB
    by any standard.

    > I was looking at this code recently because it looks really bizarre when
    > you create a half-petabyte filesystem:
    > $ sudo insmod drivers/ata/ata_ram.ko capacity=1099511627776 preallocate=0
    > [12095.028093] ata7.00: 1099511627776 sectors, multi 0: LBA48 NCQ (depth 31/32)
    > [12095.028093] ata7.00: configured for UDMA/133
    > [12095.041915] scsi 7:0:0:0: Direct-Access ATA Linux RAM Drive 0.01 PQ: 0 ANSI: 5
    > [12095.041915] sd 7:0:0:0: [sdc] Very big device. Trying to use READ CAPACITY(16).
    > [12095.041915] sd 7:0:0:0: [sdc] 1099511627776 512-byte hardware sectors (562949953 MB)
    > [12095.041915] sd 7:0:0:0: [sdc] Write Protect is off
    > [12095.041915] sd 7:0:0:0: [sdc] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA

    This looks useful for testing this... do you have an updated version?

    > 1. Avoiding 64-bit divisions is _so_ last decade. We have
    > linux/math64.h, we should use it.
    > 2. We should report in GB or TB when appropriate. The exact definition
    > of 'appropriate' is going to vary from person to person. Might I
    > suggest that we should report between two and four significant digits.
    > eg 9543 MB is ok, 10543 MB should be 10 GB.

    I've gone with five digits, it switches to GB at ~98GB, and to TB
    at ~98TB etc.

    > 3. I hate myself for saying this ... but maybe we should be using the
    > horrific MiB/GiB/TiB instead of MB/GB/TB.

    Somehow this stuff got into net-tools (ifconfig) too, so I have a
    patch to remove it from my systems.

    > 4. I've been far too busy to write said patch. Simon, would you mind
    > doing the honours?

    Sure, patch will follow this email... it can only go as far as 8192EB
    and then there's not enough space to store more than 2^64 512-byte

    (And if you only modify drivers/scsi/sd.c, the kernel make system
    won't recompile sd.o!)

    Simon Arlott

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