features/index: Optimize link-count fetching code path (#1789)

* features/index: Optimize link-count fetching code path

Problem:
AFR requests 'link-count' in lookup to check if there are any pending
heals. Based on this information, afr will set dirent->inode to NULL in
readdirp when heals are ongoing to prevent serving bad data. When heals
are completed, link-count xattr is leading to doing an opendir of
xattrop directory and then reading the contents to figure out that there
is no healing needed for every lookup. This was not detected until this
github issue because ZFS in some cases can lead to very slow readdir()
calls. Since Glusterfs does lot of lookups, this was slowing down
all operations increasing load on the system.

Code problem:
index xlator on any xattrop operation adds index to the relevant dirs
and after the xattrop operation is done, will delete/keep the index in
that directory based on the value fetched in xattrop from posix. AFR
sends all-zero xattrop for changelog xattrs. This is leading to
priv->pending_count manipulation which sets the count back to -1. Next
Lookup operation triggers opendir/readdir to find the actual link-count in
lookup because in memory priv->pending_count is -ve.

Fix:
1) Don't add to index on all-zero xattrop for a key.
2) Set pending-count to -1 when the first gfid is added into xattrop
   directory, so that the next lookup can compute the link-count.

fixes: #1764
Change-Id: I8a02c7e811a72c46d78ddb2d9d4fdc2222a444e9
Signed-off-by: Pranith Kumar K <pranith.karampuri@phonepe.com>

* addressed comments

Change-Id: Ide42bb1c1237b525d168bf1a9b82eb1bdc3bc283
Signed-off-by: Pranith Kumar K <pranith.karampuri@phonepe.com>

* tests: Handle base index absence

Change-Id: I3cf11a8644ccf23e01537228766f864b63c49556
Signed-off-by: Pranith Kumar K <pranith.karampuri@phonepe.com>

* Addressed LOCK based comments, .t comments

Change-Id: I5f53e40820cade3a44259c1ac1a7f3c5f2f0f310
Signed-off-by: Pranith Kumar K <pranith.karampuri@phonepe.com>

1 files changed, 2 insertions, 8 deletions

diff --git a/tests/bugs/replicate/bug-1722507-type-mismatch-error-handling.t b/tests/bugs/replicate/bug-1722507-type-mismatch-error-handling.t
index 1fdf7ea2da..0bd2b48cde 100644
--- a/tests/bugs/replicate/bug-1722507-type-mismatch-error-handling.t
+++ b/tests/bugs/replicate/bug-1722507-type-mismatch-error-handling.t
@@ -34,10 +34,7 @@ setfattr -n trusted.afr.$V0-client-1 -v 0x000000010000000000000001 $B0/$V0"0"/di
 setfattr -n trusted.afr.$V0-client-2 -v 0x000000010000000000000001 $B0/$V0"0"/dir
 
 # Add entry to xattrop dir to trigger index heal.
-xattrop_dir0=$(afr_get_index_path $B0/$V0"0")
-base_entry_b0=`ls $xattrop_dir0`
-gfid_str=$(gf_gfid_xattr_to_str $(gf_get_gfid_xattr $B0/$V0"0"/dir/))
-ln $xattrop_dir0/$base_entry_b0 $xattrop_dir0/$gfid_str
+TEST create_brick_xattrop_entry $B0/$V0"0" dir
 EXPECT "^1$" get_pending_heal_count $V0
 
 # Remove the gfid xattr and the link file on one brick.
@@ -82,10 +79,7 @@ setfattr -n trusted.afr.$V0-client-1 -v 0x000000010000000000000001 $B0/$V0"0"/di
 setfattr -n trusted.afr.$V0-client-2 -v 0x000000010000000000000001 $B0/$V0"0"/dir
 
 # Add entry to xattrop dir to trigger index heal.
-xattrop_dir0=$(afr_get_index_path $B0/$V0"0")
-base_entry_b0=`ls $xattrop_dir0`
-gfid_str=$(gf_gfid_xattr_to_str $(gf_get_gfid_xattr $B0/$V0"0"/dir/))
-ln $xattrop_dir0/$base_entry_b0 $xattrop_dir0/$gfid_str
+TEST create_brick_xattrop_entry $B0/$V0"0" dir
 EXPECT "^1$" get_pending_heal_count $V0
 
 # Remove the gfid xattr and the link file on two bricks.