[pbs-devel] [PATCH qemu] PVE: handle PBS write callback with big blocks correctly

[Stefan Reiter <s.reiter@proxmox.com>]

Under certain conditions QEMU will push more than the given blocksize
into the callback at once. Handle it like VMA does, by iterating the
data in PROXMOX_BACKUP_DEFAULT_CHUNK_SIZE (or smaller, for last one)
sized blocks.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---

As briefly tested by Fabian, it seems to fix the original issue.

 pve-backup.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/pve-backup.c b/pve-backup.c
index 77eb475563..4d423611e1 100644
--- a/pve-backup.c
+++ b/pve-backup.c
@@ -147,17 +147,29 @@ pvebackup_co_dump_pbs_cb(
         return -1;
     }
 
-    pbs_res = proxmox_backup_co_write_data(backup_state.pbs, di->dev_id, buf, start, size, &local_err);
-    qemu_co_mutex_unlock(&backup_state.dump_callback_mutex);
+    uint64_t transferred = 0;
+    uint64_t reused = 0;
+    while (transferred < size) {
+        uint64_t left = size - transferred;
+        uint64_t to_transfer = left < PROXMOX_BACKUP_DEFAULT_CHUNK_SIZE ?
+            left : PROXMOX_BACKUP_DEFAULT_CHUNK_SIZE;
 
-    if (pbs_res < 0) {
-        pvebackup_propagate_error(local_err);
-        return pbs_res;
-    } else {
-        size_t reused = (pbs_res == 0) ? size : 0;
-        pvebackup_add_transfered_bytes(size, !buf ? size : 0, reused);
+        pbs_res = proxmox_backup_co_write_data(backup_state.pbs, di->dev_id,
+            buf ? buf + transferred : NULL, start + transferred, to_transfer, &local_err);
+        transferred += to_transfer;
+
+        if (pbs_res < 0) {
+            pvebackup_propagate_error(local_err);
+            qemu_co_mutex_unlock(&backup_state.dump_callback_mutex);
+            return pbs_res;
+        }
+
+        reused += pbs_res == 0 ? to_transfer : 0;
     }
 
+    qemu_co_mutex_unlock(&backup_state.dump_callback_mutex);
+    pvebackup_add_transfered_bytes(size, !buf ? size : 0, reused);
+
     return size;
 }
 
-- 
2.20.1