9pfs: improve v9fs_open() tracing

Improve tracing of 9p 'Topen' request type by showing open() flags as
human-readable text.

E.g. trace output:

  v9fs_open tag 0 id 12 fid 2 mode 100352

would become:

  v9fs_open tag=0 id=12 fid=2 mode=100352(RDONLY|NONBLOCK|DIRECTORY|
  TMPFILE|NDELAY)

Therefor add a new utility function qemu_open_flags_tostr() that converts
numeric open() flags from host's native O_* flag constants to a string
presentation.

9p2000.L and 9p2000.u protocol variants use different numeric 'mode'
constants for 'Topen' requests. Instead of writing string conversion code
for both protocol variants, use the already existing conversion functions
that convert the mode flags from respective protocol constants to host's
native open() numeric flag constants and pass that result to the new
string conversion function qemu_open_flags_tostr().

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <E1tTgDR-000oRr-9g@kylie.crudebyte.com>

hw/9pfs/9p-util-generic.c

@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "qemu/osdep.h"
+#include "9p-util.h"
+#include <glib/gstrfuncs.h>
+
+char *qemu_open_flags_tostr(int flags)
+{
+    int acc = flags & O_ACCMODE;
+    return g_strconcat(
+        (acc == O_WRONLY) ? "WRONLY" : (acc == O_RDONLY) ? "RDONLY" : "RDWR",
+        (flags & O_CREAT) ? "|CREAT" : "",
+        (flags & O_EXCL) ? "|EXCL" : "",
+        (flags & O_NOCTTY) ? "|NOCTTY" : "",
+        (flags & O_TRUNC) ? "|TRUNC" : "",
+        (flags & O_APPEND) ? "|APPEND" : "",
+        (flags & O_NONBLOCK) ? "|NONBLOCK" : "",
+        (flags & O_DSYNC) ? "|DSYNC" : "",
+        #ifdef O_DIRECT
+        (flags & O_DIRECT) ? "|DIRECT" : "",
+        #endif
+        (flags & O_LARGEFILE) ? "|LARGEFILE" : "",
+        (flags & O_DIRECTORY) ? "|DIRECTORY" : "",
+        (flags & O_NOFOLLOW) ? "|NOFOLLOW" : "",
+        #ifdef O_NOATIME
+        (flags & O_NOATIME) ? "|NOATIME" : "",
+        #endif
+        #ifdef O_CLOEXEC
+        (flags & O_CLOEXEC) ? "|CLOEXEC" : "",
+        #endif
+        #ifdef __O_SYNC
+        (flags & __O_SYNC) ? "|SYNC" : "",
+        #else
+        ((flags & O_SYNC) == O_SYNC) ? "|SYNC" : "",
+        #endif
+        #ifdef O_PATH
+        (flags & O_PATH) ? "|PATH" : "",
+        #endif
+        #ifdef __O_TMPFILE
+        (flags & __O_TMPFILE) ? "|TMPFILE" : "",
+        #elif defined(O_TMPFILE)
+        ((flags & O_TMPFILE) == O_TMPFILE) ? "|TMPFILE" : "",
+        #endif
+        /* O_NDELAY is usually just an alias of O_NONBLOCK */
+        #if defined(O_NDELAY) && O_NDELAY != O_NONBLOCK
+        (flags & O_NDELAY) ? "|NDELAY" : "",
+        #endif
+        NULL /* always last (required NULL termination) */
+    );
+}

hw/9pfs/9p-util.h

@@ -267,4 +267,10 @@ int pthread_fchdir_np(int fd) __attribute__((weak_import));
 #endif
 int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev);
 
+/*
+ * Returns a newly allocated string presentation of open() flags, intended
+ * for debugging (tracing) purposes only.
+ */
+char *qemu_open_flags_tostr(int flags);
+
 #endif

hw/9pfs/9p.c

@@ -2008,6 +2008,7 @@ static void coroutine_fn v9fs_open(void *opaque)
     V9fsFidState *fidp;
     V9fsPDU *pdu = opaque;
     V9fsState *s = pdu->s;
+    g_autofree char *trace_oflags = NULL;
 
     if (s->proto_version == V9FS_PROTO_2000L) {
         err = pdu_unmarshal(pdu, offset, "dd", &fid, &mode);
@@ -2019,7 +2020,13 @@ static void coroutine_fn v9fs_open(void *opaque)
     if (err < 0) {
         goto out_nofid;
     }
-    trace_v9fs_open(pdu->tag, pdu->id, fid, mode);
+    if (trace_event_get_state_backends(TRACE_V9FS_OPEN)) {
+        trace_oflags = qemu_open_flags_tostr(
+            (s->proto_version == V9FS_PROTO_2000L) ?
+                dotl_to_open_flags(mode) : omode_to_uflags(mode)
+        );
+        trace_v9fs_open(pdu->tag, pdu->id, fid, mode, trace_oflags);
+    }
 
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {

hw/9pfs/meson.build

@@ -3,6 +3,7 @@ fs_ss.add(files(
   '9p-local.c',
   '9p-posix-acl.c',
   '9p-synth.c',
+  '9p-util-generic.c',
   '9p-xattr-user.c',
   '9p-xattr.c',
   '9p.c',

hw/9pfs/trace-events

@@ -13,7 +13,7 @@ v9fs_getattr(uint16_t tag, uint8_t id, int32_t fid, uint64_t request_mask) "tag
 v9fs_getattr_return(uint16_t tag, uint8_t id, uint64_t result_mask, uint32_t mode, uint32_t uid, uint32_t gid) "tag %d id %d getattr={result_mask %"PRId64" mode %u uid %u gid %u}"
 v9fs_walk(uint16_t tag, uint8_t id, int32_t fid, int32_t newfid, uint16_t nwnames, const char* wnames) "tag=%d id=%d fid=%d newfid=%d nwnames=%d wnames={%s}"
 v9fs_walk_return(uint16_t tag, uint8_t id, uint16_t nwnames, void* qids) "tag %d id %d nwnames %d qids %p"
-v9fs_open(uint16_t tag, uint8_t id, int32_t fid, int32_t mode) "tag %d id %d fid %d mode %d"
+v9fs_open(uint16_t tag, uint8_t id, int32_t fid, int32_t mode, const char* oflags) "tag=%d id=%d fid=%d mode=%d(%s)"
 v9fs_open_return(uint16_t tag, uint8_t id, uint8_t type, uint32_t version, uint64_t path, int iounit) "tag %u id %u qid={type %u version %u path %"PRIu64"} iounit %d"
 v9fs_lcreate(uint16_t tag, uint8_t id, int32_t dfid, int32_t flags, int32_t mode, uint32_t gid) "tag %d id %d dfid %d flags %d mode %d gid %u"
 v9fs_lcreate_return(uint16_t tag, uint8_t id, uint8_t type, uint32_t version, uint64_t path, int32_t iounit) "tag %u id %u qid={type %u version %u path %"PRIu64"} iounit %d"