From 6adfd3affda071d1083497d150a1150ade0e3fdb Mon Sep 17 00:00:00 2001 From: Neil Brown Date: Sat, 12 Jul 2008 20:27:38 +1000 Subject: [PATCH] Add some comments to explain some of the bits of superswitch. --- mdadm.h | 104 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 104 insertions(+) diff --git a/mdadm.h b/mdadm.h index 9d4f6b78..97569fad 100644 --- a/mdadm.h +++ b/mdadm.h @@ -374,27 +374,120 @@ extern char *map_dev(int major, int minor, int create); struct active_array; struct metadata_update; +/* A superswitch provides entry point the a metadata handler. + * + * The super_switch primarily operates on some "metadata" that + * is accessed via the 'supertype'. + * This metadata has one of three possible sources. + * 1/ It is read from a single device. In this case it may not completely + * describe the array or arrays as some information might be on other + * devices. + * 2/ It is read from all devices in a container. In this case all + * information is present. + * 3/ It is created by ->init_super / ->add_to_super. In this case it will + * be complete once enough ->add_to_super calls have completed. + * + * When creating an array inside a container, the metadata will be + * formed by a combination of 2 and 3. The metadata or the array is read, + * then new information is added. + * + * The metadata must sometimes have a concept of a 'current' array + * and a 'current' device. + * The 'current' array is set by init_super to be the newly created array, + * or is set by super_by_fd when it finds it is looking at an array inside + * a container. + * + * The 'current' device is either the device that the metadata was read from + * in case 1, or the last device added by add_to_super in case 3. + * Case 2 does not identify a 'current' device. + */ extern struct superswitch { + + /* Used to report details of metadata read from a component + * device. ->load_super has been called. + */ void (*examine_super)(struct supertype *st, char *homehost); void (*brief_examine_super)(struct supertype *st); void (*export_examine_super)(struct supertype *st); + + /* Used to report details of an active array. + * ->load_super was possibly given a 'component' string. + */ void (*detail_super)(struct supertype *st, char *homehost); void (*brief_detail_super)(struct supertype *st); void (*export_detail_super)(struct supertype *st); + + /* Used: + * to get uuid to storing in bitmap metadata + * and 'reshape' backup-data metadata + * To see if a device is being re-added to an array it was part of. + */ void (*uuid_from_super)(struct supertype *st, int uuid[4]); + + /* Extra generic details from metadata. This could be details about + * the container, or about an individual array within the container. + * The determination is made either by: + * load_super being given a 'component' string. + * validate_geometry determining what to create. + * getinfo_super_n really needs to be removed.. + */ void (*getinfo_super)(struct supertype *st, struct mdinfo *info); void (*getinfo_super_n)(struct supertype *st, struct mdinfo *info); + + /* Check if the given metadata is flagged as belonging to "this" + * host. For arrays that don't determine a minor-number, this + * can always be true (??) + */ int (*match_home)(struct supertype *st, char *homehost); + + /* Make one of several generic modifications to metadata + * prior to assembly (or other times). + * sparc2.2 - first bug in early 0.90 metadata + * super-minor - change name of 0.90 metadata + * summaries - 'correct' any redundant data + * resync - mark array as dirty to trigger a resync. + * uuid - set new uuid - only 0.90 or 1.x + * name - change the name of the array (where supported) + * homehost - change which host this array is tied to. + * devicesize - If metadata is at start of device, change recorded + * device size to match actual device size + * byteorder - swap bytes for 0.90 metadata + * + * force-one - mark that device as uptodate, not old or failed. + * force-array - mark array as clean if it would not otherwise + * assemble + * assemble - not sure how this is different from force-one... + * linear-grow-new - add a new device to a linear array, but don't + * change the size: so superblock still matches + * linear-grow-update - now change the size of the array. + */ int (*update_super)(struct supertype *st, struct mdinfo *info, char *update, char *devname, int verbose, int uuid_set, char *homehost); + + /* Create new metadata for new array as described. This could + * be a new container, or an array in a pre-existing container. + * Also used to zero metadata prior to writing it to invalidate old + * metadata. + */ int (*init_super)(struct supertype *st, mdu_array_info_t *info, unsigned long long size, char *name, char *homehost, int *uuid); + + /* update the metadata to include new device, either at create or + * when hot-adding a spare. + */ void (*add_to_super)(struct supertype *st, mdu_disk_info_t *dinfo, int fd, char *devname); + + /* Write metadata to one device when fixing problems or adding + * a new device. + */ int (*store_super)(struct supertype *st, int fd); + + /* Write all metadata for this array. + */ int (*write_init_super)(struct supertype *st); int (*compare_super)(struct supertype *st, struct supertype *tst); int (*load_super)(struct supertype *st, int fd, char *devname); @@ -454,6 +547,17 @@ extern struct superswitch { extern struct superswitch super_imsm; +/* A supertype holds a particular collection of metadata. + * It identifies the metadata type by the superswitch, and the particular + * sub-version of that metadata type. + * metadata read in or created is stored in 'sb' and 'info'. + * There are also fields used by mdmon to track containers. + * + * A supertype is created by: + * super_by_fd + * guess_super + * dup_super + */ struct supertype { struct superswitch *ss; int minor_version; -- 2.39.2