exofs: Multi-device mirror support
This patch changes on-disk format, it is accompanied with a parallel
patch to mkfs.exofs that enables multi-device capabilities.
After this patch, old exofs will refuse to mount a new formatted FS and
new exofs will refuse an old format. This is done by moving the magic
field offset inside the FSCB. A new FSCB *version* field was added. In
the future, exofs will refuse to mount unmatched FSCB version. To
up-grade or down-grade an exofs one must use mkfs.exofs --upgrade option
before mounting.
Introduced, a new object that contains a *device-table*. This object
contains the default *data-map* and a linear array of devices
information, which identifies the devices used in the filesystem. This
object is only written to offline by mkfs.exofs. This is why it is kept
separate from the FSCB, since the later is written to while mounted.
Same partition number, same object number is used on all devices only
the device varies.
* define the new format, then load the device table on mount time make
sure every thing is supported.
* Change I/O engine to now support Mirror IO, .i.e write same data
to multiple devices, read from a random device to spread the
read-load from multiple clients (TODO: stripe read)
Implementation notes:
A few points introduced in previous patch should be mentioned here:
* Special care was made so absolutlly all operation that have any chance
of failing are done before any osd-request is executed. This is to
minimize the need for a data consistency recovery, to only real IO
errors.
* Each IO state has a kref. It starts at 1, any osd-request executed
will increment the kref, finally when all are executed the first ref
is dropped. At IO-done, each request completion decrements the kref,
the last one to return executes the internal _last_io() routine.
_last_io() will call the registered io_state_done. On sync mode a
caller does not supply a done method, indicating a synchronous
request, the caller is put to sleep and a special io_state_done is
registered that will awaken the caller. Though also in sync mode all
operations are executed in parallel.
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
diff --git a/fs/exofs/common.h b/fs/exofs/common.h
index ce1c716..b1b178e 100644
--- a/fs/exofs/common.h
+++ b/fs/exofs/common.h
@@ -49,6 +49,7 @@
#define EXOFS_MIN_PID 0x10000 /* Smallest partition ID */
#define EXOFS_OBJ_OFF 0x10000 /* offset for objects */
#define EXOFS_SUPER_ID 0x10000 /* object ID for on-disk superblock */
+#define EXOFS_DEVTABLE_ID 0x10001 /* object ID for on-disk device table */
#define EXOFS_ROOT_ID 0x10002 /* object ID for root directory */
/* exofs Application specific page/attribute */
@@ -78,17 +79,67 @@
#define EXOFS_SUPER_MAGIC 0x5DF5
/*
- * The file system control block - stored in an object's data (mainly, the one
- * with ID EXOFS_SUPER_ID). This is where the in-memory superblock is stored
- * on disk. Right now it just has a magic value, which is basically a sanity
- * check on our ability to communicate with the object store.
+ * The file system control block - stored in object EXOFS_SUPER_ID's data.
+ * This is where the in-memory superblock is stored on disk.
*/
+enum {EXOFS_FSCB_VER = 1, EXOFS_DT_VER = 1};
struct exofs_fscb {
__le64 s_nextid; /* Highest object ID used */
- __le32 s_numfiles; /* Number of files on fs */
+ __le64 s_numfiles; /* Number of files on fs */
+ __le32 s_version; /* == EXOFS_FSCB_VER */
__le16 s_magic; /* Magic signature */
__le16 s_newfs; /* Non-zero if this is a new fs */
-};
+
+ /* From here on it's a static part, only written by mkexofs */
+ __le64 s_dev_table_oid; /* Resurved, not used */
+ __le64 s_dev_table_count; /* == 0 means no dev_table */
+} __packed;
+
+/*
+ * Describes the raid used in the FS. It is part of the device table.
+ * This here is taken from the pNFS-objects definition. In exofs we
+ * use one raid policy through-out the filesystem. (NOTE: the funny
+ * alignment at begining. We take care of it at exofs_device_table.
+ */
+struct exofs_dt_data_map {
+ __le32 cb_num_comps;
+ __le64 cb_stripe_unit;
+ __le32 cb_group_width;
+ __le32 cb_group_depth;
+ __le32 cb_mirror_cnt;
+ __le32 cb_raid_algorithm;
+} __packed;
+
+/*
+ * This is an osd device information descriptor. It is a single entry in
+ * the exofs device table. It describes an osd target lun which
+ * contains data belonging to this FS. (Same partition_id on all devices)
+ */
+struct exofs_dt_device_info {
+ __le32 systemid_len;
+ u8 systemid[OSD_SYSTEMID_LEN];
+ __le64 long_name_offset; /* If !0 then offset-in-file */
+ __le32 osdname_len; /* */
+ u8 osdname[44]; /* Embbeded, Ususally an asci uuid */
+} __packed;
+
+/*
+ * The EXOFS device table - stored in object EXOFS_DEVTABLE_ID's data.
+ * It contains the raid used for this multy-device FS and an array of
+ * participating devices.
+ */
+struct exofs_device_table {
+ __le32 dt_version; /* == EXOFS_DT_VER */
+ struct exofs_dt_data_map dt_data_map; /* Raid policy to use */
+
+ /* Resurved space For future use. Total includeing this:
+ * (8 * sizeof(le64))
+ */
+ __le64 __Resurved[4];
+
+ __le64 dt_num_devices; /* Array size */
+ struct exofs_dt_device_info dt_dev_table[]; /* Array of devices */
+} __packed;
/****************************************************************************
* inode-related things
