On Tue, 20 Sep 2022, Christoph Hellwig wrote: > On Fri, Sep 16, 2022 at 05:00:46AM -0400, Mikulas Patocka wrote: > > This patch implements REQ_OP_SECURE_ERASE and REQ_OP_WRITE_ZEROES on brd. > > Write zeroes will free the pages just like discard, but the difference is > > that it writes zeroes to the preceding and following page if the range is > > not aligned on page boundary. Secure erase is just like write zeroes, > > except that it clears the page content before freeing the page. > > What is the use case of this? And just a single overwrite is not what > storage standards would consider a secure erase, but then again we > don't really have any documentation or standards for the Linux OP, > which strongly suggests not actually implementing it for now. Without support for REQ_OP_WRITE_ZEROES, "blkdiscard -z" actually overwrites the ramdisk with zeroes and allocates all the blocks. Allocating all the blocks is pointless if we want to clear them. I implemented REQ_OP_SECURE_ERASE just because it is similar to REQ_OP_WRITE_ZEROES. Unlike disks, DRAM has no memory of previous content, so a single overwrite should be OK. We could also flush cache in REQ_OP_SECURE_ERASE, but I don't know if Linux has any portable function that does it. Mikulas
