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authorN Balachandran <nbalacha@redhat.com>2019-10-25 11:25:06 +0530
committerAmar Tumballi <amarts@gmail.com>2019-11-16 09:07:12 +0000
commitb82b1a468edbfd7a25ed3b99cc8c006a3f798cd1 (patch)
tree28d3a51d992a34297234d1029f69df829e1dd509 /xlators/cluster
parente97f01ac5c9e2774510807728e52e8acc9524a88 (diff)
cluster/dht: Add comments to the code
Add comments to the code to explain what is being done and why. Change-Id: I50831d7bd4bb73e75f6cda05fafaeb5a8619baae Updates: bz#1765421 Signed-off-by: N Balachandran <nbalacha@redhat.com>
Diffstat (limited to 'xlators/cluster')
-rw-r--r--xlators/cluster/dht/src/dht-common.c87
1 files changed, 75 insertions, 12 deletions
diff --git a/xlators/cluster/dht/src/dht-common.c b/xlators/cluster/dht/src/dht-common.c
index 98488c1..478cb48 100644
--- a/xlators/cluster/dht/src/dht-common.c
+++ b/xlators/cluster/dht/src/dht-common.c
@@ -1095,6 +1095,9 @@ out:
return 0;
}
+/* This is a gfid based nameless lookup. Without a name, the hashed subvol
+ * cannot be calculated so a lookup is sent to all subvols.
+ */
int
dht_do_discover(call_frame_t *frame, xlator_t *this, loc_t *loc)
{
@@ -1109,6 +1112,9 @@ dht_do_discover(call_frame_t *frame, xlator_t *this, loc_t *loc)
conf = this->private;
local = frame->local;
+ /* As we do not know if this is a file or directory, request
+ * both file and directory xattrs
+ */
ret = dht_set_file_xattr_req(this, loc, local->xattr_req);
if (ret) {
goto err;
@@ -1120,6 +1126,9 @@ dht_do_discover(call_frame_t *frame, xlator_t *this, loc_t *loc)
}
if (loc_is_root(loc)) {
+ /* Request the DHT commit hash xattr (trusted.glusterfs.dht.commithash)
+ * set on the brick root.
+ */
ret = dict_set_uint32(local->xattr_req, conf->commithash_xattr_name,
sizeof(uint32_t));
}
@@ -1362,7 +1371,9 @@ dht_lookup_dir_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
}
if (local->stbuf.ia_type != IA_INVAL) {
- /* This is not the first subvol to respond */
+ /* This is not the first subvol to respond
+ * Compare values to see if attrs need to be healed
+ */
if (!__is_root_gfid(stbuf->ia_gfid) &&
((local->stbuf.ia_gid != stbuf->ia_gid) ||
(local->stbuf.ia_uid != stbuf->ia_uid) ||
@@ -1387,6 +1398,9 @@ dht_lookup_dir_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
goto unlock;
}
+ /* Save the mds subvol info and stbuf. This is the value that will
+ * be used for healing
+ */
local->mds_subvol = prev;
local->mds_stbuf = *stbuf;
@@ -1400,6 +1414,7 @@ dht_lookup_dir_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
check_mds = dht_dict_get_array(xattr, conf->mds_xattr_key,
mds_xattr_val, 1, &errst);
if ((check_mds < 0) && !errst) {
+ /* Check if xattrs need to be healed on the directories */
local->mds_xattr = dict_ref(xattr);
gf_msg_debug(this->name, 0,
"%s: %s is not zero on %s. Xattrs need to be healed."
@@ -1536,6 +1551,8 @@ dht_revalidate_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
conf = this->private;
if (!conf->vch_forced) {
+ /* Update the commithash value if available
+ */
ret = dict_get_uint32(xattr, conf->commithash_xattr_name,
&vol_commit_hash);
if (ret == 0) {
@@ -1591,7 +1608,9 @@ dht_revalidate_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
}
}
- /* The GFID is missing on this subvol*/
+ /* The GFID is missing on this subvol. Lookup everywhere to force a
+ * gfid heal
+ */
if ((op_errno == ENODATA) &&
(IA_ISDIR(local->loc.inode->ia_type))) {
local->need_lookup_everywhere = 1;
@@ -1673,6 +1692,8 @@ dht_revalidate_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
local->loc.path, prev->name);
}
if ((check_mds < 0) && !errst) {
+ /* Check if xattrs need to be healed on the directory
+ */
local->mds_xattr = dict_ref(xattr);
gf_msg_debug(this->name, 0,
"Value of %s is not zero on "
@@ -1688,6 +1709,8 @@ dht_revalidate_cbk(call_frame_t *frame, void *cookie, xlator_t *this,
ret = dht_layout_dir_mismatch(this, layout, prev, &local->loc,
xattr);
if (ret != 0) {
+ /* In memory layout does not match on-disk layout.
+ */
gf_msg(this->name, GF_LOG_INFO, 0, DHT_MSG_LAYOUT_MISMATCH,
"Mismatching layouts for %s, gfid = %s", local->loc.path,
gfid);
@@ -1714,6 +1737,8 @@ unlock:
UNLOCK(&frame->lock);
if (follow_link) {
+ /* Found a linkto file. Follow it to see if the target file exists
+ */
gf_uuid_copy(local->gfid, stbuf->ia_gfid);
subvol = dht_linkfile_subvol(this, inode, stbuf, xattr);
@@ -1743,6 +1768,7 @@ unlock:
local->need_xattr_heal = 0;
if (IA_ISDIR(local->stbuf.ia_type)) {
+ /* No mds xattr found. Trigger a heal to set it */
if (!__is_root_gfid(local->loc.inode->gfid) &&
(!dict_get(local->xattr, conf->mds_xattr_key)))
local->need_selfheal = 1;
@@ -1833,11 +1859,10 @@ err:
}
int
-dht_lookup_linkfile_create_cbk(call_frame_t *frame, void *cookie,
- xlator_t *this, int32_t op_ret, int32_t op_errno,
- inode_t *inode, struct iatt *stbuf,
- struct iatt *preparent, struct iatt *postparent,
- dict_t *xdata)
+dht_lookup_linkfile_create_cbk(call_frame_t *frame, void *cooie, xlator_t *this,
+ int32_t op_ret, int32_t op_errno, inode_t *inode,
+ struct iatt *stbuf, struct iatt *preparent,
+ struct iatt *postparent, dict_t *xdata)
{
dht_local_t *local = NULL;
xlator_t *cached_subvol = NULL;
@@ -2883,6 +2908,7 @@ dht_lookup_directory(call_frame_t *frame, xlator_t *this, loc_t *loc)
}
if (!gf_uuid_is_null(local->gfid)) {
+ /* use this gfid in order to heal any missing ones */
ret = dict_set_gfuuid(local->xattr_req, "gfid-req", local->gfid, true);
if (ret)
gf_msg(this->name, GF_LOG_WARNING, 0, DHT_MSG_DICT_SET_FAILED,
@@ -3073,10 +3099,12 @@ dht_lookup_cbk(call_frame_t *frame, void *cookie, xlator_t *this, int op_ret,
* or any more call which happens from this 'loc'.
*/
if (gf_uuid_is_null(local->gfid)) {
+ /*This is set from the first successful response*/
memcpy(local->gfid, stbuf->ia_gfid, 16);
}
if (!conf->vch_forced) {
+ /* Update the commit hash in conf if it is found */
ret = dict_get_uint32(xattr, conf->commithash_xattr_name,
&vol_commit_hash);
if (ret == 0) {
@@ -3086,6 +3114,8 @@ dht_lookup_cbk(call_frame_t *frame, void *cookie, xlator_t *this, int op_ret,
is_dir = check_is_dir(inode, stbuf, xattr);
if (is_dir) {
+ /* A directory is present on all subvols, send the lookup to
+ * all subvols now */
local->inode = inode_ref(inode);
local->xattr = dict_ref(xattr);
dht_lookup_directory(frame, this, &local->loc);
@@ -3095,7 +3125,9 @@ dht_lookup_cbk(call_frame_t *frame, void *cookie, xlator_t *this, int op_ret,
is_linkfile = check_is_linkfile(inode, stbuf, xattr, conf->link_xattr_name);
if (!is_linkfile) {
- /* non-directory and not a linkfile */
+ /* non-directory and not a linkto file. This is a data file
+ * Update the layout to point to the cached subvol
+ */
ret = dht_layout_preset(this, prev, inode);
if (ret < 0) {
@@ -3109,6 +3141,9 @@ dht_lookup_cbk(call_frame_t *frame, void *cookie, xlator_t *this, int op_ret,
goto out;
}
+ /* This is a linkto file. Get the value of the target subvol from the
+ * linkto xattr and lookup there to see if the file exists
+ */
subvol = dht_linkfile_subvol(this, inode, stbuf, xattr);
if (!subvol) {
gf_msg(this->name, GF_LOG_INFO, 0, DHT_MSG_SUBVOL_INFO,
@@ -3339,6 +3374,11 @@ dht_do_revalidate(call_frame_t *frame, xlator_t *this, loc_t *loc)
}
local->mds_subvol = mds_subvol;
local->call_cnt = conf->subvolume_cnt;
+
+ /* local->call_cnt will change as responses are processed. Always use a
+ * local copy to loop through the STACK_WIND calls
+ */
+
call_cnt = local->call_cnt;
for (i = 0; i < call_cnt; i++) {
@@ -3372,6 +3412,10 @@ err:
return 0;
}
+/* If the hashed subvol is present, send the lookup to only that subvol first.
+ * If no hashed subvol, send a lookup to all subvols and proceed based on the
+ * responses.
+ */
int
dht_do_fresh_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc)
{
@@ -3411,7 +3455,8 @@ dht_do_fresh_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc)
/* Fuse sets a random value in gfid-req. If the gfid is missing
* on one or more subvols, posix will set the gfid to this value,
- * causing GFID mismatches for directories.
+ * causing GFID mismatches for directories. Remove the value fuse
+ * has sent before sending the lookup.
*/
ret = dict_get_gfuuid(local->xattr_req, "gfid-req", &local->gfid_req);
if (ret) {
@@ -3432,6 +3477,9 @@ dht_do_fresh_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc)
call_cnt = conf->subvolume_cnt;
local->call_cnt = call_cnt;
+ /* Allocate a layout. This will be populated and saved in
+ * the dht inode_ctx on successful lookup
+ */
local->layout = dht_layout_new(this, conf->subvolume_cnt);
if (!local->layout) {
op_errno = ENOMEM;
@@ -3452,7 +3500,7 @@ dht_do_fresh_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc)
return 0;
}
- /* if we have the hashed_subvol, send the lookup there first so
+ /* if the hashed_subvol is non-null, send the lookup there first so
* as to see whether we have a file or a directory */
gf_msg_debug(this->name, 0, "%s: Calling fresh lookup on %s", loc->path,
hashed_subvol->name);
@@ -3466,6 +3514,12 @@ err:
return 0;
}
+/* Depending on the input, decide if this is a:
+ * fresh-lookup: loc->name is provided but no dht inode ctx
+ * revalidation: loc->name is provided, dht inode ctx is present
+ * discover: gfid based nameless lookup.
+ */
+
int
dht_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xattr_req)
{
@@ -3518,6 +3572,10 @@ dht_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xattr_req)
/* Nameless lookup */
+ /* This is usually sent by NFS. Lookups are done based on the gfid and
+ * no name information is available. Without the name, dht cannot calculate
+ * the hash and has to send a lookup to all subvols.
+ */
if (gf_uuid_is_null(loc->pargfid) && !gf_uuid_is_null(loc->gfid) &&
!__is_root_gfid(loc->inode->gfid)) {
local->cached_subvol = NULL;
@@ -3526,6 +3584,9 @@ dht_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xattr_req)
}
if (loc_is_root(loc)) {
+ /* Request the DHT commit hash xattr (trusted.glusterfs.dht.commithash)
+ * set on the brick root.
+ */
ret = dict_set_uint32(local->xattr_req, conf->commithash_xattr_name,
sizeof(uint32_t));
}
@@ -3534,12 +3595,14 @@ dht_lookup(call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xattr_req)
hashed_subvol = dht_subvol_get_hashed(this, loc);
local->hashed_subvol = hashed_subvol;
- /* The entry has been looked up before and has an inode_ctx set
- */
if (is_revalidate(loc)) {
+ /* The entry has been looked up before and has a dht inode_ctx
+ */
dht_do_revalidate(frame, this, loc);
return 0;
} else {
+ /* Entry has not been looked up before
+ */
dht_do_fresh_lookup(frame, this, loc);
return 0;
}