9p: stat_to_qid: implement slow path

stat_to_qid attempts via qid_path_prefixmap to map unique files (which are
identified by 64 bit inode nr and 32 bit device id) to a 64 QID path value.
However this implementation makes some assumptions about inode number
generation on the host.

If qid_path_prefixmap fails, we still have 48 bits available in the QID
path to fall back to a less memory efficient full mapping.

Signed-off-by: Antonios Motakis <antonios.motakis@huawei.com>
[CS: - Rebased to https://github.com/gkurz/qemu/commits/9p-next
       (SHA1 7fc4c49e91).
     - Updated hash calls to new xxhash API.
     - Removed unnecessary parantheses in qpf_lookup_func().
     - Removed unnecessary g_malloc0() result checks.
     - Log error message when running out of prefixes in
       qid_path_fullmap().
     - Log warning message about potential degraded performance in
       qid_path_prefixmap().
     - Wrapped qpf_table initialization to dedicated qpf_table_init()
       function.
     - Fixed typo in comment. ]
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Signed-off-by: Greg Kurz <groug@kaod.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
index 7262fe80aa..35a362c0d7 100644
--- a/hw/9pfs/9p.h
+++ b/hw/9pfs/9p.h
@@ -245,6 +245,13 @@ typedef struct {
     uint16_t qp_prefix;
 } QppEntry;
 
+/* QID path full entry, as above */
+typedef struct {
+    dev_t dev;
+    ino_t ino;
+    uint64_t path;
+} QpfEntry;
+
 struct V9fsState
 {
     QLIST_HEAD(, V9fsPDU) free_list;
@@ -268,7 +275,9 @@ struct V9fsState
     V9fsQID root_qid;
     dev_t dev_id;
     struct qht qpp_table;
+    struct qht qpf_table;
     uint16_t qp_prefix_next;
+    uint64_t qp_fullpath_next;
 };
 
 /* 9p2000.L open flags */