[Xen-changelog] [xen stable-4.6] oxenstored: Quota.merge: don't assume domain already exists

[patchbot@xxxxxxx]

commit ba391da2e7c68aad131159c90733e0d39b85ed37
Author:     Jonathan Davies <jonathan.davies@xxxxxxxxxx>
AuthorDate: Wed Nov 11 11:21:53 2015 +0000
Commit:     Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CommitDate: Tue Jan 19 13:41:21 2016 +0000

    oxenstored: Quota.merge: don't assume domain already exists
    
    In Quota.merge, we merge two quota hashtables, orig_quota and mod_quota, 
putting
    the results into dest_quota. These hashtables map domids to the number of
    entries currently owned by that domain.
    
    When mod_quota contains an entry for a domid that was not present in 
orig_quota
    (or dest_quota), the call to get_entry caused Quota.merge to raise a 
Not_found
    exception. This propagates back to the client as an ENOENT error, which is 
not
    an appropriate return value from some operations, such as transaction_end.
    
    This situation can arise when a transaction that introduces a domain (hence
    calling Quota.add_entry) needs to be coalesced due to concurrent xenstore
    activity.
    
    This patch handles the merge in the case where mod_quota contains an entry 
not
    present in orig_quota (or in dest_quota) by treating that hashtable as 
having
    existing value 0.
    
    Signed-off-by: Jonathan Davies <jonathan.davies@xxxxxxxxxx>
    Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
    (cherry picked from commit 82ff7cbed64e3cc094d6812b3ad672c660649969)
---
 tools/ocaml/xenstored/quota.ml |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/ocaml/xenstored/quota.ml b/tools/ocaml/xenstored/quota.ml
index e6953c6..abcac91 100644
--- a/tools/ocaml/xenstored/quota.ml
+++ b/tools/ocaml/xenstored/quota.ml
@@ -83,6 +83,6 @@ let add quota diff =
        Hashtbl.iter (fun id nb -> set_entry quota id (get_entry quota id + 
nb)) diff.cur
 
 let merge orig_quota mod_quota dest_quota =
-         Hashtbl.iter (fun id nb -> let diff = nb - (get_entry orig_quota id) 
in
+         Hashtbl.iter (fun id nb -> let diff = nb - (try get_entry orig_quota 
id with Not_found -> 0) in
                                if diff <> 0 then
-                                       set_entry dest_quota id ((get_entry 
dest_quota id) + diff)) mod_quota.cur
+                                       set_entry dest_quota id ((try get_entry 
dest_quota id with Not_found -> 0) + diff)) mod_quota.cur
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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