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SubjectRE: [linux-usb-devel] Kernel unable to read partition table on US B Memory Key
On Wed, 6 Jul 2005, Roberts-Thomson, James wrote:

> Alan,
>
> > Try putting delays at various spots in sd_revalidate_disk:
> > the beginning, the middle, and the end.
>
> OK, the attached patch works for me when sd_mod was loaded with delay_use=1.
>
> Now I'm quite prepared to be told that this is a really horrible and
> inapproprate hack (given that I am not a kernel developer, I don't really
> know the "correct" way to solve this problem); and I'll cheerfully admit
> that it doesn't really solve the problem cleanly as can be seen below:

It would have been better simply to call msleep, but never mind.

> Jul 6 14:44:52 pc196344 kernel: sd: waiting for device to get ready.
> Jul 6 14:44:53 pc196344 kernel: sda: Unit Not Ready, sense:
> Jul 6 14:44:53 pc196344 kernel: : Current: sense key: Unit Attention
> Jul 6 14:44:53 pc196344 kernel: Additional sense: Not ready to ready
> change, medium may have changed
> Jul 6 14:44:53 pc196344 kernel: sda : READ CAPACITY failed.
> Jul 6 14:44:53 pc196344 kernel: sda : status=1, message=00, host=0,
> driver=08
> Jul 6 14:44:53 pc196344 kernel: sd: Current: sense key: Unit Attention
> Jul 6 14:44:53 pc196344 kernel: Additional sense: Not ready to ready
> change, medium may have changed
> Jul 6 14:44:53 pc196344 kernel: sda: test WP failed, assume Write Enabled
> Jul 6 14:44:53 pc196344 kernel: sda: assuming drive cache: write through

> Jul 6 14:44:53 pc196344 kernel: sd: waiting for device to get ready.
> Jul 6 14:44:54 pc196344 kernel: sda: Unit Not Ready, sense:
> Jul 6 14:44:54 pc196344 kernel: : Current: sense key: Unit Attention
> Jul 6 14:44:54 pc196344 kernel: Additional sense: Not ready to ready
> change, medium may have changed
> Jul 6 14:44:54 pc196344 kernel: sda : READ CAPACITY failed.
> Jul 6 14:44:54 pc196344 kernel: sda : status=1, message=00, host=0,
> driver=08
> Jul 6 14:44:54 pc196344 kernel: sd: Current: sense key: Unit Attention
> Jul 6 14:44:54 pc196344 kernel: Additional sense: Not ready to ready
> change, medium may have changed
> Jul 6 14:44:54 pc196344 kernel: sda: test WP failed, assume Write Enabled
> Jul 6 14:44:54 pc196344 kernel: sda: assuming drive cache: write through

> Jul 6 14:44:54 pc196344 kernel: sd: waiting for device to get ready.
> Jul 6 14:44:55 pc196344 kernel: SCSI device sda: 255488 512-byte hdwr
> sectors (131 MB)
> Jul 6 14:44:55 pc196344 kernel: sda: Write Protect is off
> Jul 6 14:44:55 pc196344 kernel: sda: Mode Sense: 03 00 00 00
> Jul 6 14:44:55 pc196344 kernel: sda: assuming drive cache: write through
> Jul 6 14:44:55 pc196344 kernel: /dev/scsi/host5/bus0/target0/lun0: p1
> Jul 6 14:44:55 pc196344 kernel: Attached scsi removable disk sda at scsi5,
> channel 0, id 0, lun 0
>
> There are three delays from my patch in the above list,

Yes. Why are there three instead of just one? The sd_revalidate_disk
routine should only be called once (although a bug in recent kernels
causes it to be called twice).

> and increasing the
> delay to 3 seconds didn't help, as I got three one-second delays.

I don't understand. Why didn't you get three three-second delays?

> However, if someone with the appropriate knowledge could transform my kludge
> into a proper fix, then I would be very happy.

Can you try adding delays before, after, and inbetween the calls to
sd_read_capacity, sd_read_write_protect_flag, and sd_read_cache_type, all
near the end of sd_revalidate_disk?

> Alan, thanks very much for your help - I really appreciate the quick
> responses you have given me.
>
> Note that I now have the output from the USB Snoop tool under Windows if
> anyone wants it - please ask if needed to help solve the issue "correctly".

Can you make it available on a web or ftp site and post the URL for
interested parties?

Alan Stern

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