fs/dirent: add d_ino member to struct dirent

Add the POSIX d_ino (file serial number) member to struct dirent and
populate it on every readdir() path, so portable callers (e.g. scp in
dropbear) that read dp->d_ino observe a meaningful, non-zero inode
number:

  - include/dirent.h: declare d_ino in struct dirent and drop the
    outdated comment claiming the field is unimplemented.
  - include/nuttx/fs/hostfs.h: add d_ino to struct nuttx_dirent_s so
    the hostfs ABI can carry the inode number across the VFS boundary.
  - arch/sim/src/sim/posix/sim_hostfs.c: forward the host's
    ent->d_ino into entry->d_ino.
  - fs/vfs/fs_dir.c (read_pseudodir): copy the in-memory inode's
    i_ino into entry->d_ino for the pseudo filesystem.
  - fs/yaffs/yaffs_vfs.c: forward yaffs's dirent->d_ino into
    entry->d_ino.
  - fs/rpmsgfs: extend struct rpmsgfs_readdir_s with an 'ino' field
    and propagate it across the RPC in both rpmsgfs_server (fills it
    from the underlying entry) and rpmsgfs_client (writes it back to
    the caller's nuttx_dirent_s).

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

arch/sim/src/sim/posix/sim_hostfs.c

@@ -443,6 +443,8 @@ int host_readdir(void *dirp, struct nuttx_dirent_s *entry)
       strncpy(entry->d_name, ent->d_name, sizeof(entry->d_name) - 1);
       entry->d_name[sizeof(entry->d_name) - 1] = 0;
 
+      entry->d_ino = ent->d_ino;
+
       /* Map the type */
 
       if (ent->d_type == DT_REG)

fs/rpmsgfs/rpmsgfs.h

@@ -166,6 +166,7 @@ begin_packed_struct struct rpmsgfs_readdir_s
 {
   struct rpmsgfs_header_s header;
   int32_t                 fd;
+  uint32_t                ino;
   uint32_t                type;
   char                    name[0];
 } end_packed_struct;

fs/rpmsgfs/rpmsgfs_client.c

@@ -209,6 +209,7 @@ static int rpmsgfs_readdir_handler(FAR struct rpmsg_endpoint *ept,
     {
       strlcpy(entry->d_name, rsp->name, sizeof(entry->d_name));
       entry->d_type = rsp->type;
+      entry->d_ino = rsp->ino;
     }
 
   rpmsg_post(ept, &cookie->sem);

fs/rpmsgfs/rpmsgfs_server.c

@@ -622,6 +622,7 @@ static int rpmsgfs_readdir_handler(FAR struct rpmsg_endpoint *ept,
           size = MIN(size - len, strlen(entry->d_name) + 1);
           msg->type = entry->d_type;
           strlcpy(msg->name, entry->d_name, size);
+          msg->ino = entry->d_ino;
           len += size;
           ret = 0;
         }

fs/vfs/fs_dir.c

@@ -376,6 +376,8 @@ static int read_pseudodir(FAR struct fs_dirent_s *dir,
       entry->d_type = DTYPE_DIRECTORY;
     }
 
+  entry->d_ino = pdir->next->i_ino;
+
   /* Now get the inode to visit next time that readdir() is called */
 
   inode_lock();

include/dirent.h

@@ -107,11 +107,12 @@
  * of char containing at least {NAME_MAX} plus one elements.
  *
  * POSIX also requires the field d_ino (type ino_t) that provides the file
- * serial number.  This functionality is not implemented in NuttX.
+ * serial number.
  */
 
 struct dirent
 {
+  ino_t    d_ino;                 /* File serial number */
   uint8_t  d_type;                /* Type of file */
   char     d_name[NAME_MAX + 1];  /* File name */
 };

include/nuttx/fs/hostfs.h

@@ -150,6 +150,7 @@ struct nuttx_timespec
 
 struct nuttx_dirent_s
 {
+  nuttx_ino_t  d_ino;
   uint8_t      d_type;                      /* type of file */
   char         d_name[CONFIG_NAME_MAX + 1]; /* filename */
 };