On 4/25/20 12:31 AM, Coly Li wrote: > On 2020/3/26 23:28, Jason Baron wrote: >> Let's add some CONFIG_* options to directly configure the raid0 layout >> if you know in advance how your raid0 array was created. This can be >> simpler than having to manage module or kernel command-line parameters. >> > > Hi Jason, > > If the people who compiling the kernel is not the end users, the > communication gap has potential risk to make users to use a different > layout for existing raid0 array after a kernel upgrade. > > If this patch goes into upstream, it is very probably such risky > situation may happen. > > The purpose of adding default_layout is to let *end user* to be aware of > they layout when they use difference sizes component disks to assemble > the raid0 array, and make decision which layout algorithm should be > used. Such situation cannot be decided in kernel compiling time. I agree that in general it may not be known at compile time. Thus, I've left the default as RAID0_LAYOUT_NONE. However, there are use-cases where it is known at compile-time which layout is needed. In our use-case, we knew that we didn't have any pre-3.14 raid0 arrays. Thus, we can safely set RAID0_ALT_MULTIZONE_LAYOUT. So this is a simpler configuration for us than setting module or command line parameters. Thanks, -Jason > >> If the raid0 array was created by a pre-3.14 kernel, use >> RAID0_ORIG_LAYOUT. If the raid0 array was created by a 3.14 or newer >> kernel then select RAID0_ALT_MULTIZONE_LAYOUT. Otherwise, the default >> setting is RAID0_LAYOUT_NONE, in which case the current behavior of >> needing to specify a module parameter raid0.default_layout=1|2 is >> preserved. >> > > The difficulty is for a given md raid0 array, there is no clue whether > it is built on pre-3.14 kernel or not. If the kernel is not configured > and built by end user, we have risk that wrong algorithm will be applied > to unmatched layout. >> Thanks. > > Coly Li > > >> Cc: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx> >> Cc: NeilBrown <neilb@xxxxxxx> >> Cc: Song Liu <songliubraving@xxxxxx> >> Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx> >> --- >> drivers/md/Kconfig | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ >> drivers/md/raid0.c | 7 +++++++ >> 2 files changed, 62 insertions(+) >> >> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig >> index d6d5ab2..c0c6d82 100644 >> --- a/drivers/md/Kconfig >> +++ b/drivers/md/Kconfig >> @@ -79,6 +79,61 @@ config MD_RAID0 >> >> If unsure, say Y. >> >> +choice >> + prompt "RAID0 Layout" >> + default RAID0_LAYOUT_NONE >> + depends on MD_RAID0 >> + help >> + A change was made in Linux 3.14 that unintentinally changed the >> + the layout for RAID0. This can result in data corruption if a pre-3.14 >> + and a 3.14 or later kernel both wrote to the array. However, if the >> + devices in the array are all of the same size then the layout would >> + have been unaffected by this change, and there is no risk of data >> + corruption from this issue. >> + >> + Unfortunately, the layout can not be determined by the kernel. If the >> + array has only been written to by a 3.14 or later kernel its safe to >> + set RAID0_ALT_MULTIZONE_LAYOUT. If its only been written to by a >> + pre-3.14 kernel its safe to select RAID0_ORIG_LAYOUT. If its been >> + written by both then select RAID0_LAYOUT_NONE, which will not >> + configure the array. The array can then be examined for corruption. >> + >> + For new arrays you may choose either layout version. Neither version >> + is inherently better than the other. >> + >> + Alternatively, these parameters can also be specified via the module >> + parameter raid0.default_layout=<N>. N=2 selects the 'new' or multizone >> + layout, while N=1 selects the 'old' layout or original layout. If >> + unset the array will not be configured. >> + >> + The layout can also be written directly to the raid0 array via the >> + mdadm command, which can be auto-detected by the kernel. See: >> + <https://www.kernel.org/doc/html/latest/admin-guide/md.html#multi-zone-raid0-layout-migration> >> + >> +config RAID0_ORIG_LAYOUT >> + bool "raid0 layout for arrays only written to by a pre-3.14 kernel" >> + help >> + If the raid0 array was only created and written to by a pre-3.14 kernel. >> + >> +config RAID0_ALT_MULTIZONE_LAYOUT >> + bool "raid0 layout for arrays only written to be a 3.14 or newer kernel" >> + help >> + If the raid0 array was only created and written to by a 3.14 or later >> + kernel. >> + >> +config RAID0_LAYOUT_NONE >> + bool "raid0 layout must be specified via a module parameter" >> + help >> + If a raid0 array was written to by both a pre-3.14 and a 3.14 or >> + later kernel, you may have data corruption. This option will not >> + auto configure the array and thus you can examine the array offline >> + to determine the best way to proceed. With RAID0_LAYOUT_NONE >> + set, the choice for raid0 layout can be set via a module parameter >> + raid0.default_layout=<N>. Or the layout can be written directly >> + to the raid0 array via the mdadm command. >> + >> +endchoice >> + >> config MD_RAID1 >> tristate "RAID-1 (mirroring) mode" >> depends on BLK_DEV_MD >> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c >> index 322386f..576eaa6 100644 >> --- a/drivers/md/raid0.c >> +++ b/drivers/md/raid0.c >> @@ -19,7 +19,14 @@ >> #include "raid0.h" >> #include "raid5.h" >> >> +#if defined(CONFIG_RAID0_ORIG_LAYOUT) >> +static int default_layout = RAID0_ORIG_LAYOUT; >> +#elif defined(CONFIG_RAID0_ALT_MULTIZONE_LAYOUT) >> +static int default_layout = RAID0_ALT_MULTIZONE_LAYOUT; >> +#else >> static int default_layout = 0; >> +#endif >> + >> module_param(default_layout, int, 0644); >> >> #define UNSUPPORTED_MDDEV_FLAGS \ >> >
