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-rw-r--r--drivers/block/nbd.c13
1 files changed, 12 insertions, 1 deletions
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index fdee7567fd15..f533f3375e24 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -754,9 +754,20 @@ static int __init nbd_init(void)
return -ENOMEM;
part_shift = 0;
- if (max_part > 0)
+ if (max_part > 0) {
part_shift = fls(max_part);
+ /*
+ * Adjust max_part according to part_shift as it is exported
+ * to user space so that user can know the max number of
+ * partition kernel should be able to manage.
+ *
+ * Note that -1 is required because partition 0 is reserved
+ * for the whole disk.
+ */
+ max_part = (1UL << part_shift) - 1;
+ }
+
if ((1UL << part_shift) > DISK_MAX_PARTS)
return -EINVAL;
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