dd is the method I know. I'm going to ask around.

Are you looking to completely zero the SD card or just wipe out the partition table?

(Here is a link for wiping the partition table)
https://www.chrisnewland.com/linux-wipe-sd-card-partition-table-277


adam

We want to completely zero the SD card as fast as possible; dd is too slow.
I see there are MMC command codes in mmc.h (e.g. MMC_ERASE), but I have not found online a document which describes exactly how to do this.
Thanks.
Matt

I have asked a colleague, but he isn't aware of how to do this. I've asked a couple other Linux guys as well. I'll let you know if/what they have to report.

adam

I see there is an 'mmc_erase' function inside the mmc driver code located in:
./rpm/BUILD/linux-3.0/drivers/mmc/core/core.c
But I cannot see how this can be called from user application code as I see no mention of it in the include files used by the app code.
Do you think it is reasonable to update the driver code to react to a custom ioctl command code and execute this mmc_erase() function within the driver code ?

Our developer is out, and I am not sure when he comes back, but I did a little searching and I found some patches that were submitted in 2010.

They may not cleanly apply, but I think it's in the general direction you want.

https://groups.google.com/forum/#!topic/linux.kernel/MATo4Wf9kdU

The patch explictly states it's will: Add ability to do MMC erase and secure erase operations from userspace, using the BLKDISCARD ioctl and a newly created BLKSECDISCARD ioctl.

I don't believe these were ever fully accepted into the linux community, so I would use them at your own risk.

adam

OK - Great! I will try that out and post a reply on how it goes.
In the mmc driver code, I noticed that it checked on a flag 'REQ_DISCARD' but that appeared to be on the code which serviced I/O requests on the device and not ioctl commands, and I couldn't figure out how user space code would be able to cause this flag to be set in a write command.

Thanks so much for the tip on BLKDISCARD !
I found source code online to build a 'blkdiscard' console app and using it to wipe the card with BLKDISCARD worked very fast (2 sec for 7.6 GB card. Cannot confirm whether all data was really wiped this fast or the command returns before h/w io is actually complete....looking at the driver source code it appears to be synchronous but I was astonished at how fast this went.). With the SD card I am using the BLKSECDISCARD variant resulted in 'not supported' error but I don't think I need that.

That's fantastic! I am glad it worked out. Let us know if you have any other questions or issues.

adam