debug(fat32): read 打印文件状态(size/first_cluster/pos)与实际读取字节数，定位 ehdr 读取失败根因

VKernel/Kernel/drivers/fs/fat32/fat32_types.vp

@@ -4,7 +4,8 @@ import spinlock
 import string
 import fat32_diskio as diskio
 import fat32_time as ftime
-
+import viperlib
+import drivers.serial.uart.serial as serial
 
 def _read32(buf: t.CUInt8T | t.CPtr, off: t.CUInt32T) -> t.CUInt32T:
 	return t.CUInt32T(buf[off]) | (t.CUInt32T(buf[off + 1]) << 8) | (t.CUInt32T(buf[off + 2]) << 16) | (t.CUInt32T(buf[off + 3]) << 24)
@@ -1452,6 +1453,11 @@ class fileobj:
 		if not self.is_open:                   return FRESULT.FR_INVALID_OBJECT
 		if not (self.flags & FA_READ):         return FRESULT.FR_DENIED
 		c.Set(t.CUInt32T(br, t.CPtr), 0)
+		# [RD-DIAG] 定位 read_len<64（ehdr 读取失败）根因：打印文件状态
+		_rdb: t.CArray[t.CChar, 160]
+		viperlib.snprintf(c.Addr(_rdb), 160, "[fat32] read: size=%lu fc=%lu cc=%lu pos=%lu btr=%lu\n",
+		                  self.file_size, self.first_cluster, self.current_cluster, self.file_pos, btr)
+		serial.puts(c.Addr(_rdb))
 		vol: volinfo | t.CPtr = self.vol
 		remaining:   t.CUInt32T = btr
 		buf_ptr:     t.CUInt8T | t.CPtr = t.CUInt8T(buff, t.CPtr)
@@ -1487,6 +1493,10 @@ class fileobj:
 				next_c: t.CUInt32T = vol.cluster_get_next(self.current_cluster)
 				if next_c == 0: break
 				self.current_cluster = next_c
+		# [RD-DIAG] 打印实际读取字节数
+		_rdb2: t.CArray[t.CChar, 96]
+		viperlib.snprintf(c.Addr(_rdb2), 96, "[fat32] read done: br=%lu\n", total_read)
+		serial.puts(c.Addr(_rdb2))
 		c.Set(t.CUInt32T(br, t.CPtr), total_read)
 		return FRESULT.FR_OK