p9: set filetype from directory to file in lcreate

The 9p lcreate operation takes a directory fid as input and creates a
file in that directory; when the operation completes, the same fid
becomes a reference to the newly-created file. We updated the internal
self.fids structure's file and path fields to point to the new file, but
we neglected to update the filetype field, which would remain as the
original FileType::Directory.

This caused an issue with commit 53cd18e062 ("p9: use *at() functions
for set_attr"), since that change causes set_attr requests to validate
the filetype is not a directory when attempting to set its length.

BUG=b:253838039
TEST=tast run <...>.DefaultSharedFolder

Change-Id: Ie46a660dd4616d669c924014e704e9b5703eb7e9
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3983116
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

common/p9/src/server/mod.rs

@@ -711,6 +711,7 @@ impl Server {
         let iounit = st.st_blksize as u32;
 
         fid.file = Some(file);
+        fid.filetype = FileType::Regular;
 
         // This fid now refers to the newly created file so we need to update the O_PATH fd for it
         // as well.

common/p9/src/server/tests.rs

@@ -1276,3 +1276,41 @@ create_test!(
 );
 create_test!(append_read_write_file_create, P9_APPEND | P9_RDWR, 0o600u32);
 create_test!(append_wronly_file_create, P9_APPEND | P9_WRONLY, 0o600u32);
+
+#[test]
+fn lcreate_set_len() {
+    let (test_dir, mut server) = setup("lcreate_set_len");
+
+    let name = "foo.txt";
+    let fid = ROOT_FID + 1;
+    create(
+        &mut server,
+        &*test_dir,
+        ROOT_FID,
+        fid,
+        name,
+        P9_RDWR,
+        0o600u32,
+    )
+    .expect("failed to create file");
+
+    let tsetattr = Tsetattr {
+        fid,
+        valid: 0x8, // P9_SETATTR_SIZE
+        size: 100,
+        // The other fields are not used because the relevant flags aren't set in `valid`.
+        mode: 0,
+        uid: 0,
+        gid: 0,
+        atime_sec: 0,
+        atime_nsec: 0,
+        mtime_sec: 0,
+        mtime_nsec: 0,
+    };
+    server
+        .set_attr(&tsetattr)
+        .expect("failed to set file length after lcreate");
+
+    let tclunk = Tclunk { fid };
+    server.clunk(&tclunk).expect("Unable to clunk file");
+}