aboutsummaryrefslogtreecommitdiff
path: root/net/ceph/osdmap.c
AgeCommit message (Collapse)AuthorFilesLines
2016-07-28libceph: rados pool namespace supportGravatar Yan, Zheng 1-6/+46
Add pool namesapce pointer to struct ceph_file_layout and struct ceph_object_locator. Pool namespace is used by when mapping object to PG, it's also used when composing OSD request. The namespace pointer in struct ceph_file_layout is RCU protected. So libceph can read namespace without taking lock. Signed-off-by: Yan, Zheng <zyan@redhat.com> [idryomov@gmail.com: ceph_oloc_destroy(), misc minor changes] Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-07-28libceph: define new ceph_file_layout structureGravatar Yan, Zheng 1-3/+3
Define new ceph_file_layout structure and rename old ceph_file_layout to ceph_file_layout_legacy. This is preparation for adding namespace to ceph_file_layout structure. Signed-off-by: Yan, Zheng <zyan@redhat.com>
2016-07-22libceph: apply new_state before new_up_client on incrementalsGravatar Ilya Dryomov 1-43/+113
Currently, osd_weight and osd_state fields are updated in the encoding order. This is wrong, because an incremental map may look like e.g. new_up_client: { osd=6, addr=... } # set osd_state and addr new_state: { osd=6, xorstate=EXISTS } # clear osd_state Suppose osd6's current osd_state is EXISTS (i.e. osd6 is down). After applying new_up_client, osd_state is changed to EXISTS | UP. Carrying on with the new_state update, we flip EXISTS and leave osd6 in a weird "!EXISTS but UP" state. A non-existent OSD is considered down by the mapping code 2087 for (i = 0; i < pg->pg_temp.len; i++) { 2088 if (ceph_osd_is_down(osdmap, pg->pg_temp.osds[i])) { 2089 if (ceph_can_shift_osds(pi)) 2090 continue; 2091 2092 temp->osds[temp->size++] = CRUSH_ITEM_NONE; and so requests get directed to the second OSD in the set instead of the first, resulting in OSD-side errors like: [WRN] : client.4239 192.168.122.21:0/2444980242 misdirected client.4239.1:2827 pg 2.5df899f2 to osd.4 not [1,4,6] in e680/680 and hung rbds on the client: [ 493.566367] rbd: rbd0: write 400000 at 11cc00000 (0) [ 493.566805] rbd: rbd0: result -6 xferred 400000 [ 493.567011] blk_update_request: I/O error, dev rbd0, sector 9330688 The fix is to decouple application from the decoding and: - apply new_weight first - apply new_state before new_up_client - twiddle osd_state flags if marking in - clear out some of the state if osd is destroyed Fixes: http://tracker.ceph.com/issues/14901 Cc: stable@vger.kernel.org # 3.15+: 6dd74e44dc1d: libceph: set 'exists' flag for newly up osd Cc: stable@vger.kernel.org # 3.15+ Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Reviewed-by: Josh Durgin <jdurgin@redhat.com>
2016-05-30libceph: use %s instead of %pE in dout()sGravatar Ilya Dryomov 1-2/+2
Commit d30291b985d1 ("libceph: variable-sized ceph_object_id") changed dout()s in what is now encode_request() and ceph_object_locator_to_pg() to use %pE, mostly to document that, although all rbd and cephfs object names are NULL-terminated strings, ceph_object_id will handle any RADOS object name, including the one containing NULs, just fine. However, it turns out that vbin_printf() can't handle anything but ints and %s - all %p suffixes are ignored. The buffer %p** points to isn't recorded, resulting in trash in the messages if the buffer had been reused by the time bstr_printf() got to it. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: allocate dummy osdmap in ceph_osdc_init()Gravatar Ilya Dryomov 1-5/+18
This leads to a simpler osdmap handling code, particularly when dealing with pi->was_full, which is introduced in a later commit. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: introduce ceph_osd_request_target, calc_target()Gravatar Ilya Dryomov 1-0/+121
Introduce ceph_osd_request_target, containing all mapping-related fields of ceph_osd_request and calc_target() for calculating mappings and populating it. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: pi->min_size, pi->last_force_request_resendGravatar Ilya Dryomov 1-1/+47
Add and decode pi->min_size and pi->last_force_request_resend. These are going to be used by calc_target(). Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: make pgid_cmp() globalGravatar Ilya Dryomov 1-11/+12
calc_target() code is going to need to know how to compare PGs. Take lhs and rhs pgid by const * while at it. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: rename ceph_calc_pg_primary()Gravatar Ilya Dryomov 1-4/+5
Rename ceph_calc_pg_primary() to ceph_pg_to_acting_primary() to emphasise that it returns acting primary. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: ceph_osds, ceph_pg_to_up_acting_osds()Gravatar Ilya Dryomov 1-125/+179
Knowning just acting set isn't enough, we need to be able to record up set as well to detect interval changes. This means returning (up[], up_len, up_primary, acting[], acting_len, acting_primary) and passing it around. Introduce and switch to ceph_osds to help with that. Rename ceph_calc_pg_acting() to ceph_pg_to_up_acting_osds() and return both up and acting sets from it. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: rename ceph_oloc_oid_to_pg()Gravatar Ilya Dryomov 1-15/+16
Rename ceph_oloc_oid_to_pg() to ceph_object_locator_to_pg(). Emphasise that returned is raw PG and return -ENOENT instead of -EIO if the pool doesn't exist. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: nuke unused fields and functionsGravatar Ilya Dryomov 1-2/+1
Either unused or useless: osdmap->mkfs_epoch osd->o_marked_for_keepalive monc->num_generic_requests osdc->map_waiters osdc->last_requested_map osdc->timeout_tid osd_req_op_cls_response_data() osdmap_apply_incremental() @msgr arg Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-05-26libceph: variable-sized ceph_object_idGravatar Ilya Dryomov 1-1/+92
Currently ceph_object_id can hold object names of up to 100 (CEPH_MAX_OID_NAME_LEN) characters. This is enough for all use cases, expect one - long rbd image names: - a format 1 header is named "<imgname>.rbd" - an object that points to a format 2 header is named "rbd_id.<imgname>" We operate on these potentially long-named objects during rbd map, and, for format 1 images, during header refresh. (A format 2 header name is a small system-generated string.) Lift this 100 character limit by making ceph_object_id be able to point to an externally-allocated string. Apart from being able to work with almost arbitrarily-long named objects, this allows us to reduce the size of ceph_object_id from >100 bytes to 64 bytes. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2016-02-04crush: decode and initialize chooseleaf_stableGravatar Ilya Dryomov 1-5/+14
Also add missing \n while at it. Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Reviewed-by: Sage Weil <sage@redhat.com>
2015-09-08libceph: set 'exists' flag for newly up osdGravatar Yan, Zheng 1-1/+1
Signed-off-by: Yan, Zheng <zyan@redhat.com> Reviewed-by: Sage Weil <sage@redhat.com> Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2015-07-01crush: fix a bug in tree bucket decodeGravatar Ilya Dryomov 1-1/+1
struct crush_bucket_tree::num_nodes is u8, so ceph_decode_8_safe() should be used. -Wconversion catches this, but I guess it went unnoticed in all the noise it spews. The actual problem (at least for common crushmaps) isn't the u32 -> u8 truncation though - it's the advancement by 4 bytes instead of 1 in the crushmap buffer. Fixes: http://tracker.ceph.com/issues/2759 Cc: stable@vger.kernel.org Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Reviewed-by: Josh Durgin <jdurgin@redhat.com>
2015-04-22crush: straw2 bucket type with an efficient 64-bit crush_ln()Gravatar Ilya Dryomov 1-0/+25
This is an improved straw bucket that correctly avoids any data movement between items A and B when neither A nor B's weights are changed. Said differently, if we adjust the weight of item C (including adding it anew or removing it completely), we will only see inputs move to or from C, never between other items in the bucket. Notably, there is not intermediate scaling factor that needs to be calculated. The mapping function is a simple function of the item weights. The below commits were squashed together into this one (mostly to avoid adding and then yanking a ~6000 lines worth of crush_ln_table): - crush: add a straw2 bucket type - crush: add crush_ln to calculate nature log efficently - crush: improve straw2 adjustment slightly - crush: change crush_ln to provide 32 more digits - crush: fix crush_get_bucket_item_weight and bucket destroy for straw2 - crush/mapper: fix divide-by-0 in straw2 (with div64_s64() for draw = ln / w and INT64_MIN -> S64_MIN - need to create a proper compat.h in ceph.git) Reflects ceph.git commits 242293c908e923d474910f2b8203fa3b41eb5a53, 32a1ead92efcd351822d22a5fc37d159c65c1338, 6289912418c4a3597a11778bcf29ed5415117ad9, 35fcb04e2945717cf5cfe150b9fa89cb3d2303a1, 6445d9ee7290938de1e4ee9563912a6ab6d8ee5f, b5921d55d16796e12d66ad2c4add7305f9ce2353. Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
2014-10-14libceph: Convert pr_warning to pr_warnGravatar Joe Perches 1-10/+10
Use the more common pr_warn. Other miscellanea: o Coalesce formats o Realign arguments Signed-off-by: Joe Perches <joe@perches.com> Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
2014-10-14libceph: fix a use after free issue in osdmap_set_max_osdGravatar Li RongQing 1-16/+16
If the state variable is krealloced successfully, map->osd_state will be freed, once following two reallocation failed, and exit the function without resetting map->osd_state, map->osd_state become a wild pointer. fix it by resetting them after krealloc successfully. Signed-off-by: Li RongQing <roy.qing.li@gmail.com> Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
2014-05-16crush: decode and initialize chooseleaf_vary_rGravatar Ilya Dryomov 1-0/+5
Commit e2b149cc4ba0 ("crush: add chooseleaf_vary_r tunable") added the crush_map::chooseleaf_vary_r field but missed the decode part. This lead to misdirected requests caused by incorrect raw crush mapping sets. Fixes: http://tracker.ceph.com/issues/8226 Reported-and-Tested-by: Dmitry Smirnov <onlyjob@member.fsf.org> Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Sage Weil <sage@inktank.com>
2014-04-28libceph: fix non-default values check in apply_primary_affinity()Gravatar Ilya Dryomov 1-4/+5
osd_primary_affinity array is indexed into incorrectly when checking for non-default primary-affinity values. This nullifies the impact of the rest of the apply_primary_affinity() and results in misdirected requests. if (osds[i] != CRUSH_ITEM_NONE && osdmap->osd_primary_affinity[i] != ^^^ CEPH_OSD_DEFAULT_PRIMARY_AFFINITY) { For a pool with size 2, this always ends up checking osd0 and osd1 primary_affinity values, instead of the values that correspond to the osds in question. E.g., given a [2,3] up set and a [max,max,0,max] primary affinity vector, requests are still sent to osd2, because both osd0 and osd1 happen to have max primary_affinity values and therefore we return from apply_primary_affinity() early on the premise that all osds in the given set have max (default) values. Fix it. Fixes: http://tracker.ceph.com/issues/7954 Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Sage Weil <sage@inktank.com>
2014-04-04libceph: output primary affinity values on osdmap updatesGravatar Ilya Dryomov 1-0/+2
Similar to osd weights, output primary affinity values on incremental osdmap updates. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
2014-04-04libceph: redo ceph_calc_pg_primary() in terms of ceph_calc_pg_acting()Gravatar Ilya Dryomov 1-75/+4
Reimplement ceph_calc_pg_primary() in terms of ceph_calc_pg_acting() and get rid of the now unused calc_pg_raw(). Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: add support for osd primary affinityGravatar Ilya Dryomov 1-0/+68
Respond to non-default primary_affinity values accordingly. (Primary affinity allows the admin to shift 'primary responsibility' away from specific osds, effectively shifting around the read side of the workload and whatever overhead is incurred by peering and writes by virtue of being the primary). Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: add support for primary_temp mappingsGravatar Ilya Dryomov 1-1/+6
Change apply_temp() to override primary in the same way pg_temp overrides osd set. primary_temp overrides pg_temp primary too. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: return primary from ceph_calc_pg_acting()Gravatar Ilya Dryomov 1-8/+12
In preparation for adding support for primary_temp, stop assuming primaryness: add a primary out parameter to ceph_calc_pg_acting() and change call sites accordingly. Primary is now specified separately from the order of osds in the set. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: switch ceph_calc_pg_acting() to new helpersGravatar Ilya Dryomov 1-13/+38
Switch ceph_calc_pg_acting() to new helpers: pg_to_raw_osds(), raw_to_up_osds() and apply_temps(). Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: introduce apply_temps() helperGravatar Ilya Dryomov 1-0/+52
apply_temp() helper for applying various temporary mappings (at this point only pg_temp mappings) to the up set, therefore transforming it into an acting set. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: introduce pg_to_raw_osds() and raw_to_up_osds() helpersGravatar Ilya Dryomov 1-0/+76
pg_to_raw_osds() helper for computing a raw (crush) set, which can contain non-existant and down osds. raw_to_up_osds() helper for pruning non-existant and down osds from the raw set, therefore transforming it into an up set, and determining up primary. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: primary_affinity decode bitsGravatar Ilya Dryomov 1-0/+72
Add two helpers to decode primary_affinity (full map, vector<u32>) and new_primary_affinity (inc map, map<u32, u32>) and switch to them. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: primary_affinity infrastructureGravatar Ilya Dryomov 1-0/+47
Add primary_affinity infrastructure. primary_affinity values are stored in an max_osd-sized array, hanging off ceph_osdmap, similar to a osd_weight array. Introduce {get,set}_primary_affinity() helpers, primarily to return CEPH_OSD_DEFAULT_PRIMARY_AFFINITY when no affinity has been set and to abstract out osd_primary_affinity array allocation and initialization. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: primary_temp decode bitsGravatar Ilya Dryomov 1-0/+69
Add a common helper to decode both primary_temp (full map, map<pg_t, u32>) and new_primary_temp (inc map, same) and switch to it. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: primary_temp infrastructureGravatar Ilya Dryomov 1-1/+9
Add primary_temp mappings infrastructure. struct ceph_pg_mapping is overloaded, primary_temp mappings are stored in an rb-tree, rooted at ceph_osdmap, in a manner similar to pg_temp mappings. Dump primary_temp mappings to /sys/kernel/debug/ceph/<client>/osdmap, one 'primary_temp <pgid> <osd>' per line, e.g: primary_temp 2.6 4 Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: generalize ceph_pg_mappingGravatar Ilya Dryomov 1-4/+4
In preparation for adding support for primary_temp mappings, generalize struct ceph_pg_mapping so it can hold mappings other than pg_temp. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: introduce get_osdmap_client_data_v()Gravatar Ilya Dryomov 1-16/+65
Full and incremental osdmaps are structured identically and have identical headers. Add a helper to decode both "old" (16-bit version, v6) and "new" (8-bit struct_v+struct_compat+struct_len, v7) osdmap enconding headers and switch to it. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: introduce decode{,_new}_pg_temp() and switch to themGravatar Ilya Dryomov 1-72/+67
Consolidate pg_temp (full map, map<pg_t, vector<u32>>) and new_pg_temp (inc map, same) decoding logic into a common helper and switch to it. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: switch osdmap_set_max_osd() to krealloc()Gravatar Ilya Dryomov 1-15/+17
Use krealloc() instead of rolling our own. (krealloc() with a NULL first argument acts as a kmalloc()). Properly initalize the new array elements. This is needed to make future additions to osdmap easier. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: introduce decode{,_new}_pools() and switch to themGravatar Ilya Dryomov 1-37/+57
Consolidate pools (full map, map<u64, pg_pool_t>) and new_pools (inc map, same) decoding logic into a common helper and switch to it. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: rename __decode_pool{,_names}() to decode_pool{,_names}()Gravatar Ilya Dryomov 1-6/+8
To be in line with all the other osdmap decode helpers. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: fix and clarify ceph_decode_need() sizesGravatar Ilya Dryomov 1-6/+7
Sum up sizeof(...) results instead of (incorrectly) hard-coding the number of bytes, expressed in ints and longs. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: nuke bogus encoding version check in osdmap_apply_incremental()Gravatar Ilya Dryomov 1-5/+4
Only version 6 of osdmap encoding is supported, anything other than version 6 results in an error and halts the decoding process. Checking if version is >= 5 is therefore bogus. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: fixup error handling in osdmap_apply_incremental()Gravatar Ilya Dryomov 1-32/+34
The existing error handling scheme requires resetting err to -EINVAL prior to calling any ceph_decode_* macro. This is ugly and fragile, and there already are a few places where we would return 0 on error, due to a missing reset. Follow osdmap_decode() and fix this by adding a special e_inval label to be used by all ceph_decode_* macros. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: fix crush_decode() call site in osdmap_decode()Gravatar Ilya Dryomov 1-5/+2
The size of the memory area feeded to crush_decode() should be limited not only by osdmap end, but also by the crush map length. Also, drop unnecessary dout() (dout() in crush_decode() conveys the same info) and step past crush map only if it is decoded successfully. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: check length of osdmap osd arraysGravatar Ilya Dryomov 1-4/+10
Check length of osd_state, osd_weight and osd_addr arrays. They should all have exactly max_osd elements after the call to osdmap_set_max_osd(). Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: safely decode max_osd value in osdmap_decode()Gravatar Ilya Dryomov 1-2/+4
max_osd value is not covered by any ceph_decode_need(). Use a safe version of ceph_decode_* macro to decode it. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: fixup error handling in osdmap_decode()Gravatar Ilya Dryomov 1-26/+27
The existing error handling scheme requires resetting err to -EINVAL prior to calling any ceph_decode_* macro. This is ugly and fragile, and there already are a few places where we would return 0 on error, due to a missing reset. Fix this by adding a special e_inval label to be used by all ceph_decode_* macros. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: split osdmap allocation and decode stepsGravatar Ilya Dryomov 1-15/+29
Split osdmap allocation and initialization into a separate function, ceph_osdmap_decode(). Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-04libceph: dump osdmap and enhance output on decode errorsGravatar Ilya Dryomov 1-6/+15
Dump osdmap in hex on both full and incremental decode errors, to make it easier to match the contents with error offset. dout() map epoch and max_osd value on success. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Alex Elder <elder@linaro.org>
2014-04-03libceph: a per-osdc crush scratch bufferGravatar Ilya Dryomov 1-9/+16
With the addition of erasure coding support in the future, scratch variable-length array in crush_do_rule_ary() is going to grow to at least 200 bytes on average, on top of another 128 bytes consumed by rawosd/osd arrays in the call chain. Replace it with a buffer inside struct osdmap and a mutex. This shouldn't result in any contention, because all osd requests were already serialized by request_mutex at that point; the only unlocked caller was ceph_ioctl_get_dataloc(). Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Sage Weil <sage@inktank.com>
2014-01-27libceph: follow {read,write}_tier fields on osd request submissionGravatar Ilya Dryomov 1-3/+25
Overwrite ceph_osd_request::r_oloc.pool with read_tier for read ops and write_tier for write and read+write ops (aka basic tiering support). {read,write}_tier are part of pg_pool_t since v9. This commit bumps our pg_pool_t decode compat version from v7 to v9, all new fields except for {read,write}_tier are ignored. Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com> Reviewed-by: Sage Weil <sage@inktank.com>