On Sat, Jan 18, 2020 at 9:35 AM Coly Li <colyli@xxxxxxx> wrote: > > On 2020/1/18 8:22 下午, Clodoaldo Neto wrote: > > On Sat, Jan 18, 2020 at 7:54 AM Clodoaldo Neto > > <clodoaldo.pinto.neto@xxxxxxxxx> wrote: > >> > >> On Thu, Jan 16, 2020 at 9:59 PM Coly Li <colyli@xxxxxxx> wrote: > >>> > >>> On 2020/1/17 5:52 上午, Clodoaldo Neto wrote: > >>>> > >>>> Em seg, 13 de jan de 2020 11:19, Coly Li <colyli@xxxxxxx > >>>> <mailto:colyli@xxxxxxx>> escreveu: > >>>>> > >>>>> On 2020/1/13 8:44 下午, Jens-U. Mozdzen wrote: > >>>>>> Hi Coly, > >>>>>> > >>>>>> jumping in here, because I was looking for a way to revert from bcache > >>>>>> to plain device: > >>>>>> > >>>>>> Zitat von Coly Li <colyli@xxxxxxx <mailto:colyli@xxxxxxx>>: > >>>>>>> The super block location of the backing disk is occupied by bcache. You > >>>>>>> cannot mount the file system directly from the backing disk which is > >>>>>>> formated as bcache backing device [...] (bcache offset all I/Os on > >>>>>>> bcache device 4KB behind the requesting > >>>>>>> LBA on backing disk). > >>>>>> > >>>>>> Assuming that no caching device is associated with a backing device (so > >>>>>> the backing device is "clean" as in "containing all data blocks with the > >>>>>> current content"), could one convert the content of a backing device to > >>>>>> a "non-bcached device" by removing the first 4096 octets of the backing > >>>>>> device content? > >>>>>> > >>>>>> Something like "dd if=backingdev of=newdev skip_bytes=4096 ..."? > >>>>> > >>>>> Hi Jens-U, > >>>>> > >>>>> you may try dmsetup to setup a linear device mapper target, and the map > >>>>> table just skipping the first 4KB (bcache superblock area). If you are > >>>>> lucky, I mean the real file system is not corrupted, the created device > >>>>> mapper target can be mounted directly. > >>>> > >>>> > >>>> I'm trying dmsetup but it does not accept anything other than 0 and 0 > >>>> at the beginning and end of the table: > >>>> > >>>> # echo '0 3774578672 linear /dev/mapper/backing-device 8' | dmsetup > >>>> create dmb > >>>> device-mapper: reload ioctl on dmb failed: Invalid argument > >>>> Command failed. > >>> > >>> The above line should work, if 3774578672 is a correct size number in > >>> sectors. > >> > >> I took it from the original map: > >> > >> # dmsetup table /dev/mapper/backing-device > >> 0 3774578672 crypt aes-xts-plain64 > >> :64:logon:cryptsetup:7e2c0b40-8dec-4b13-8d00-b53b55160775-d0 0 251:0 > >> 32768 > > > > It works like this: > > > > # echo '0 3774578664 linear /dev/mapper/backing-device 8' | dmsetup create dmb > > > > But then I can't mount it: > > > > # mount /dev/mapper/dmb /r > > mount: /r: wrong fs type, bad option, bad superblock on > > /dev/mapper/dmb, missing codepage or helper program, or other error. > > It might be my fault, from bcache-tools, it seems the offset is > BDEV_DATA_START_DEFAULT (16 sectors). How about: > # echo '0 3774578656 linear /dev/mapper/backing-device 16' | dmsetup > create dmb Still no luck # echo '0 3774578656 linear /dev/mapper/backing-device 16' | dmsetup create dmb # mount /dev/mapper/dmb /r mount: /r: wrong fs type, bad option, bad superblock on /dev/mapper/dmb, missing codepage or helper program, or other error. Clodoaldo > > > -- > > Coly Li
