[PATCH v2 3/6] ksmbd: send inline FinderInfo in FIND responses when READDIR_ATTR negotiated

["Gaël Blivet-Bailly" <gael.blivet@gmail.com>]

From: Gael Blivet <gael.blivet@gmail.com>

Without READDIR_ATTR, macOS Finder resolves type/creator/icon for
every file in a directory listing by opening its AFP_AfpInfo stream
individually -- one extra CREATE+QUERY_INFO+CLOSE round trip per file,
which is the dominant cost of browsing a large directory over SMB from
a Mac.

When the client negotiates READDIR_ATTR (conn->aapl_readdir_attr, set
during CREATE's AAPL context exchange), inline the same information
directly into each FILEID_BOTH_DIRECTORY_INFORMATION FIND entry:
  EaSize           = max_access, expanded specific rights
                      (GENERIC_ALL_FLAGS), not the raw FILE_GENERIC_ALL_LE
                      "generic" meta-bit -- that bit has none of the
                      specific FILE_* rights macOS's smbfs.kext checks
                      bit-by-bit, so reporting it directly would fail
                      every access check and show Finder's "no entry"
                      badge on every file/folder.
  ShortNameLength  = 24 (fixed; the spec says 0 when there's no short
                      name; kept for wire parity with Samba, see below)
  ShortName[0..7]  = resource fork size (0 -- no resource forks)
  ShortName[8..23] = compressed FinderInfo (all zero: type/creator
                      unset, client falls back to extension-based
                      icon/type detection, consistent with the
                      AFP_AfpInfo synthesis this mirrors)
  Reserved2        = Unix mode bits
Reparse-point status is still carried via ExtFileAttributes rather
than EaSize once READDIR_ATTR is active, since EaSize is repurposed
for max_access.

Reverse-engineered from macOS smbfs.kext network behavior and
cross-checked against Samba's vfs_fruit marshalling
(source3/smbd/smb2_trans2.c, SMB_FIND_ID_BOTH_DIRECTORY_INFO). Also
confirmed against Apple's published SMBClient kernel source
(apple-oss-distributions/SMBClient, smb_smb_2.c) -- every field here
matches exactly, except ShortNameLength=24: real V1 clients read but
never examine that field, so it's kept for wire parity with Samba, not
because macOS requires it.

Signed-off-by: Gael Blivet <gael.blivet@gmail.com>
---
v1 -> v2: Cross-checked wire format against Apple's published
SMBClient kernel source -- confirmed every field matches, and
corrected an inaccurate claim about ShortNameLength=24 being
something real clients require (they don't; a comment-only fix).

 fs/smb/server/smb2pdu.c | 60 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 55 insertions(+), 5 deletions(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 8fed5fd6d..120c2c80d 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -4733,17 +4733,67 @@ static int smb2_populate_readdir_entry(struct ksmbd_conn *conn, int info_level,
 
 		fibdinfo = (struct file_id_both_directory_info *)kstat;
 		fibdinfo->FileNameLength = cpu_to_le32(conv_len);
-		fibdinfo->EaSize =
-			smb2_get_reparse_tag_special_file(ksmbd_kstat->kstat->mode);
-		if (fibdinfo->EaSize)
-			fibdinfo->ExtFileAttributes = FILE_ATTRIBUTE_REPARSE_POINT_LE;
 		if (conn->is_aapl)
 			fibdinfo->UniqueId = 0;
 		else
 			fibdinfo->UniqueId = cpu_to_le64(ksmbd_kstat->kstat->ino);
 		fibdinfo->ShortNameLength = 0;
 		fibdinfo->Reserved = 0;
-		fibdinfo->Reserved2 = cpu_to_le16(0);
+		if (conn->aapl_readdir_attr) {
+			/*
+			 * READDIR_ATTR wire format, confirmed against Samba's
+			 * vfs_fruit marshalling (source3/smbd/smb2_trans2.c):
+			 *   EaSize           = max_access (expanded specific
+			 *                      rights, simplified to "grant all")
+			 *   ShortNameLength  = 24 (fixed; not 0, despite the spec)
+			 *   ShortName[0..7]  = resource fork size (uint64 LE, 0 = no rfork)
+			 *   ShortName[8..23] = compressed FinderInfo (type+creator+flags+
+			 *                      ext_flags+date_added, 16 bytes LE; all
+			 *                      zeros means type=0/creator=0, i.e. use
+			 *                      the file extension for icon lookup)
+			 *   Reserved2        = Unix mode bits (uint16 LE)
+			 * Reparse-point tag is indicated via ExtFileAttributes, not EaSize.
+			 */
+			__le32 reparse_tag =
+				smb2_get_reparse_tag_special_file(ksmbd_kstat->kstat->mode);
+
+			if (reparse_tag)
+				fibdinfo->ExtFileAttributes = FILE_ATTRIBUTE_REPARSE_POINT_LE;
+			/*
+			 * FILE_GENERIC_ALL_LE (0x10000000) is the raw
+			 * "generic all" meta-bit -- valid only in a
+			 * client's requested access mask, for the server
+			 * to expand. It has none of the specific FILE_*
+			 * rights bits set (FILE_LIST_DIRECTORY, FILE_TRAVERSE,
+			 * etc.), so reporting it here as max_access would make
+			 * macOS's bit-by-bit access checks fail on every
+			 * entry -> permanent "no entry" badges in Finder.
+			 * Report the actual expanded rights instead, same
+			 * as smb_map_generic_desired_access() does when
+			 * translating a client's GENERIC_ALL request.
+			 */
+			fibdinfo->EaSize = cpu_to_le32(GENERIC_ALL_FLAGS);
+			/*
+			 * The spec says ShortNameLength should be 0 when
+			 * there's no short name; 24 here instead matches
+			 * Samba's vfs_fruit marshalling (smb2_trans2.c) for
+			 * server-to-server wire parity. Apple's own SMBClient
+			 * source (smb_smb_2.c) confirms real macOS clients
+			 * read this field but never examine its value for a
+			 * V1 (non-READDIR_ATTR_V2) connection -- V2 repurposes
+			 * it as a flags field that is interpreted; V1 doesn't.
+			 * Either value is safe here, so keep 24 for parity.
+			 */
+			fibdinfo->ShortNameLength = 24;
+			memset(fibdinfo->ShortName, 0, sizeof(fibdinfo->ShortName));
+			fibdinfo->Reserved2 = cpu_to_le16(ksmbd_kstat->kstat->mode & 0xffff);
+		} else {
+			fibdinfo->EaSize =
+				smb2_get_reparse_tag_special_file(ksmbd_kstat->kstat->mode);
+			if (fibdinfo->EaSize)
+				fibdinfo->ExtFileAttributes = FILE_ATTRIBUTE_REPARSE_POINT_LE;
+			fibdinfo->Reserved2 = cpu_to_le16(0);
+		}
 		if (d_info->hide_dot_file && d_info->name[0] == '.')
 			fibdinfo->ExtFileAttributes |= FILE_ATTRIBUTE_HIDDEN_LE;
 		memcpy(fibdinfo->FileName, conv_name, conv_len);
-- 
2.43.0