semantic: 0.986
other: 0.985
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PID: 0.981
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KVM: 0.914

SD card size constraint conceptually wrong

The patch discussed here:
https://<email address hidden>/msg720833.html
introduces an artificial size constraint for SD cards
that has no relation to reality.

I'm trying to use an _actual_ **physical** SD card,
and qemu tells me its size is "invalid".

Something here appears to be conceptually wrong.

--------------------------------------------------
# fdisk -l /dev/sdg
Disk /dev/sdg: 14.84 GiB, 15931539456 bytes, 31116288 sectors
Disk model: USB  SD Reader  
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x7a0c8bb0

Device     Boot  Start      End  Sectors  Size Id Type
/dev/sdg1         2048   524287   522240  255M  c W95 FAT32 (LBA)
/dev/sdg2       524288 31116287 30592000 14.6G 83 Linux
# qemu-system-aarch64 -M raspi3 -m 1G -kernel vmlinuz-5.4.79-v8 -dtb bcm2837-rpi-3-b-plus.dtb -append console=ttyAMA0\ root=/dev/mmcblk0p2\ rw -nographic -serial mon:stdio -drive file=/dev/sdg,format=raw
qemu-system-aarch64: Invalid SD card size: 14.8 GiB
SD card size has to be a power of 2, e.g. 16 GiB.
You can resize disk images with 'qemu-img resize <imagefile> <new-size>'
(note that this will lose data if you make the image smaller than it currently is).
--------------------------------------------------

The same invocation with a dump of the actual image
resized to match qemu's odd expectations works fine.


This is on QEMU 5.2.0, as evidenced by the following:
--------------------------------------------------
# qemu-system-aarch64 -version
QEMU emulator version 5.2.0
Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers
--------------------------------------------------

Is there a simple workaround that disables this rather
arbitrary constraint?

On 1/7/21 8:24 PM, - wrote:
> Public bug reported:
> 
> The patch discussed here:
> https://<email address hidden>/msg720833.html
> introduces an artificial size constraint for SD cards
> that has no relation to reality.
> 
> I'm trying to use an _actual_ **physical** SD card,
> and qemu tells me its size is "invalid".
> 
> Something here appears to be conceptually wrong.
> 
> --------------------------------------------------
> # fdisk -l /dev/sdg
> Disk /dev/sdg: 14.84 GiB, 15931539456 bytes, 31116288 sectors
> Disk model: USB  SD Reader  
> Units: sectors of 1 * 512 = 512 bytes
> Sector size (logical/physical): 512 bytes / 512 bytes
> I/O size (minimum/optimal): 512 bytes / 512 bytes
> Disklabel type: dos
> Disk identifier: 0x7a0c8bb0
> 
> Device     Boot  Start      End  Sectors  Size Id Type
> /dev/sdg1         2048   524287   522240  255M  c W95 FAT32 (LBA)
> /dev/sdg2       524288 31116287 30592000 14.6G 83 Linux
> # qemu-system-aarch64 -M raspi3 -m 1G -kernel vmlinuz-5.4.79-v8 -dtb bcm2837-rpi-3-b-plus.dtb -append console=ttyAMA0\ root=/dev/mmcblk0p2\ rw -nographic -serial mon:stdio -drive file=/dev/sdg,format=raw
> qemu-system-aarch64: Invalid SD card size: 14.8 GiB
> SD card size has to be a power of 2, e.g. 16 GiB.

Your physical card likely is 16GiB. The firmware running
on it is free to reserve some amount to replace broken
blocks. In your case ~7%.

We choose to restrict the model to the physical layer to
simplify the design and avoid to deal with security issues.

Patches to improve the model by better matching the real
world are always welcomed!

> You can resize disk images with 'qemu-img resize <imagefile> <new-size>'
> (note that this will lose data if you make the image smaller than it currently is).

Indeed, we can remove this warning for block devices.

> --------------------------------------------------
> 
> The same invocation with a dump of the actual image
> resized to match qemu's odd expectations works fine.
> 
> 
> This is on QEMU 5.2.0, as evidenced by the following:
> --------------------------------------------------
> # qemu-system-aarch64 -version
> QEMU emulator version 5.2.0
> Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers
> --------------------------------------------------
> 
> Is there a simple workaround that disables this rather
> arbitrary constraint?

No, but you can send a patch :)

Regards,

Phil.


> Indeed, we can remove this warning for block devices.

Couldn't you simply remove the entire size check logic for block devices?

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
valid, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes
anymore).

Thank you and sorry for the inconvenience.


On Wed, May 12, 2021 at 11:08:09AM -0000, Thomas Huth wrote:
> 
> If it is not fixed yet and you think that this bug report here is still
> valid, then you have two options:

Actually, you seem to have forgotten a third option: I simply don't care
enough, especially after the patronizing response to my original report,
to bother.



This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'invalid' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/297