cluster/dht: avoid overwriting client writes during migration

For more details on this issue see
https://github.com/gluster/glusterfs/issues/308

Solution:
This is a restrictive solution where a file will not be migrated
if a client writes to it during the migration. This does not
check if the writes from the rebalance and the client actually
do overlap.

If dht_writev_cbk finds that the file is being migrated (PHASE1)
it will set an xattr on the destination file indicating the file
was updated by a non-rebalance client.
Rebalance checks if any other client has written to the dst file
and aborts the file migration if it finds the xattr.

updates gluster/glusterfs#308

Change-Id: I73aec28bc9dbb8da57c7425ec88c6b6af0fbc9dd
Signed-off-by: Susant Palai <spalai@redhat.com>
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Signed-off-by: N Balachandran <nbalacha@redhat.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/xlators/storage/posix/src/posix-helpers.c b/xlators/storage/posix/src/posix-helpers.c
index 90afced604c..56c9b4afe94 100644
--- a/xlators/storage/posix/src/posix-helpers.c
+++ b/xlators/storage/posix/src/posix-helpers.c
@@ -2739,3 +2739,45 @@ posix_override_umask (mode_t mode, mode_t mode_bit)
         gf_msg_debug ("posix", 0, "The value of mode is %u", mode);
         return mode;
 }
+
+int
+posix_check_internal_writes (xlator_t *this, fd_t *fd, int sysfd,
+                             dict_t *xdata)
+{
+        int          ret = 0;
+        size_t       xattrsize = 0;
+        data_t      *val = NULL;
+
+        LOCK (&fd->inode->lock);
+        {
+                val = dict_get (xdata, GF_PROTECT_FROM_EXTERNAL_WRITES);
+                if (val) {
+                        ret = sys_fsetxattr (sysfd,
+                                             GF_PROTECT_FROM_EXTERNAL_WRITES,
+                                             val->data, val->len, 0);
+                        if (ret == -1) {
+                                gf_msg (this->name, GF_LOG_ERROR,
+                                        P_MSG_XATTR_FAILED,
+                                        errno, "setxattr failed key %s",
+                                        GF_PROTECT_FROM_EXTERNAL_WRITES);
+                        }
+
+                        goto out;
+                }
+
+                if (dict_get (xdata, GF_AVOID_OVERWRITE)) {
+                        xattrsize = sys_fgetxattr (sysfd,
+                                                   GF_PROTECT_FROM_EXTERNAL_WRITES,
+                                                   NULL, 0);
+                        if ((xattrsize == -1) && ((errno == ENOATTR) ||
+                            (errno == ENODATA))) {
+                                ret = 0;
+                        } else {
+                                ret = -1;
+                        }
+                }
+        }
+out:
+        UNLOCK (&fd->inode->lock);
+        return ret;
+}