9pfs: Don't use file descriptors in core code

v9fs_getattr() currently peeks into V9fsFidOpenState to know if a fid
has a valid file descriptor or directory stream. Even though the fields
are accessible, this is an implementation detail of the local backend
that should not be manipulated directly by the server code.

Abstract that with a new has_valid_file_handle() backend operation.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <20250312152933.383967-3-groug@kaod.org>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>

4 files changed, 21 insertions, 3 deletions

diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h
index 4997677..b815cea4 100644
--- a/fsdev/file-op-9p.h
+++ b/fsdev/file-op-9p.h
@@ -164,6 +164,7 @@ struct FileOperations {
     int (*renameat)(FsContext *ctx, V9fsPath *olddir, const char *old_name,
                     V9fsPath *newdir, const char *new_name);
     int (*unlinkat)(FsContext *ctx, V9fsPath *dir, const char *name, int flags);
+    bool (*has_valid_file_handle)(int fid_type, V9fsFidOpenState *fs);
 };
 
 #endif
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index 99b9560..b161322 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -1572,6 +1572,13 @@ static int local_parse_opts(QemuOpts *opts, FsDriverEntry *fse, Error **errp)
     return 0;
 }
 
+static bool local_has_valid_file_handle(int fid_type, V9fsFidOpenState *fs)
+{
+    return
+        (fid_type == P9_FID_FILE && fs->fd != -1) ||
+        (fid_type == P9_FID_DIR && fs->dir.stream != NULL);
+}
+
 FileOperations local_ops = {
     .parse_opts = local_parse_opts,
     .init  = local_init,
@@ -1609,4 +1616,5 @@ FileOperations local_ops = {
     .name_to_path = local_name_to_path,
     .renameat  = local_renameat,
     .unlinkat = local_unlinkat,
+    .has_valid_file_handle = local_has_valid_file_handle,
 };
diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c
index 2abaf3a..be0492b 100644
--- a/hw/9pfs/9p-synth.c
+++ b/hw/9pfs/9p-synth.c
@@ -615,6 +615,11 @@ static int synth_init(FsContext *ctx, Error **errp)
     return 0;
 }
 
+static bool synth_has_valid_file_handle(int fid_type, V9fsFidOpenState *fs)
+{
+    return false;
+}
+
 FileOperations synth_ops = {
     .init         = synth_init,
     .lstat        = synth_lstat,
@@ -650,4 +655,5 @@ FileOperations synth_ops = {
     .name_to_path = synth_name_to_path,
     .renameat     = synth_renameat,
     .unlinkat     = synth_unlinkat,
+    .has_valid_file_handle = synth_has_valid_file_handle,
 };
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 80b190f..4586822 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1593,6 +1593,11 @@ out_nofid:
     pdu_complete(pdu, err);
 }
 
+static bool fid_has_valid_file_handle(V9fsState *s, V9fsFidState *fidp)
+{
+    return s->ops->has_valid_file_handle(fidp->fid_type, &fidp->fs);
+}
+
 static void coroutine_fn v9fs_getattr(void *opaque)
 {
     int32_t fid;
@@ -1615,9 +1620,7 @@ static void coroutine_fn v9fs_getattr(void *opaque)
         retval = -ENOENT;
         goto out_nofid;
     }
-    if ((fidp->fid_type == P9_FID_FILE && fidp->fs.fd != -1) ||
-        (fidp->fid_type == P9_FID_DIR && fidp->fs.dir.stream))
-    {
+    if (fid_has_valid_file_handle(pdu->s, fidp)) {
         retval = v9fs_co_fstat(pdu, fidp, &stbuf);
     } else {
         retval = v9fs_co_lstat(pdu, &fidp->path, &stbuf);