geo-rep: rename handling in dht volume

Background:

Glusterfs changelogs are stored in each brick, which records the changes
happened in that brick. Georep will run in all the nodes of master and
processes changelogs "independently".
Processing changelogs is in brick level, but all the fops will be replayed
on "slave mount" point.

Problem:
With a DHT volume, in changelog "internal fops" are NOT recorded.
For Rename case, Rename is recorded in "hashed" brick changelog.
(DHT's internal fops like creating linkto file, unlink is NOT recorded).
This lead us to inconsistent rename operations.

For example,
Distribute volume created with Two bricks B1, B2.

//Consider master volume mounted @ /mnt/master
and following operations executed:
cd /mnt/master
touch f1 // f1 falls on B1 Hash
mv f1 f2 // f2 falls on B2 Hash

// Here, Changelogs are recorded as below:
@B1
CREATE f1
@B2
RENAME f1 f2

Here, race exists between Brick B1 and B2, say B2 will get executed first.
Source file f1 itself is "NOT PRESENT", so it will go ahead and create
f2 (Current implementation).
We have this problem When rename falls in another brick and
file is unlinked in Master.

Similar kind of issue exists in following case too(multiple rename):
CREATE f1
RENAME f1 f2
RENAME f2 f1

Solution:

Instead of carrying out "changelogging" at "HASHED volume",
carry out  at the "CACHED volume".
This way we have rename operations carried out where actual files are present.
So,Changelog recorded as :
@B1
CREATE f1
RENAME f1 f2

credit: sarumuga@redhat.com

PS: Some of the races as the one below are _NOT_ fixed by this patch

* f1 and f2 exist. B1 and B2 are their respective cached subvols. For 
both files hashed-subvol == cached-subvol
* mv f1 f2 on master.
* B1 has change-log entry of rename f1 f2
* rebalance migrates f2 from B1 and B2
* mv f2 f1 on master.
* B2 has change-log entry of rename f2 f1

Since changelog entries (rename f1 f2) and (rename f2 f1) are processed 
independently by gsyncds, which of either f1 and f2 survives on slave 
is subject to race. Note that on master its file f1 with name f1 which 
survived. On slave it can be either file f1 with name f1 or file f2 
with name f2 based on who wins the race of processing changelog.


Change-Id: Iebc222f582613924c3a7cba37fb6d3e2d8332eda
BUG: 1141379
Signed-off-by: Nithya Balachandran <nbalacha@redhat.com>
Reviewed-on: http://review.gluster.org/10410
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Tested-by: NetBSD Build System
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>
Tested-by: Raghavendra G <rgowdapp@redhat.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/libglusterfs/src/common-utils.h b/libglusterfs/src/common-utils.h
index e8b5fc8359..c361405d5e 100644
--- a/libglusterfs/src/common-utils.h
+++ b/libglusterfs/src/common-utils.h
@@ -130,6 +130,31 @@ enum _gf_xlator_ipc_targets {
 typedef enum _gf_boolean gf_boolean_t;
 typedef enum _gf_client_pid gf_client_pid_t;
 typedef enum _gf_xlator_ipc_targets _gf_xlator_ipc_targets_t;
+
+/* The DHT file rename operation is not a straightforward rename.
+ * It involves creating linkto and linkfiles, and can unlink or rename the
+ * source file depending on the hashed and cached subvols for the source
+ * and target files. this makes it difficult for geo-rep to figure out that
+ * a rename operation has taken place.
+ *
+ * We now send a special key and the values of the source and target pargfids
+ * and basenames to indicate to changelog that the operation in question
+ * should be treated as a rename. We are explicitly filling and sending this
+ * as a binary value in the dictionary as the unlink op will not have the
+ * source file information. The lengths of the src and target basenames
+ * are used to calculate where to start reading the names in the structure.
+ * XFS allows a max of 255 chars for filenames but other file systems might
+ * not have such restrictions
+ */
+typedef struct dht_changelog_rename_info {
+         uuid_t  old_pargfid;
+         uuid_t  new_pargfid;
+         int32_t oldname_len;
+         int32_t newname_len;
+         char    buffer[1];
+ } dht_changelog_rename_info_t;
+
+
 typedef int (*gf_cmp) (void *, void *);
 
 void gf_global_variable_init(void);