fs/inode: add optional manual FD backtrace control via task group flag

When CONFIG_FS_BACKTRACE is enabled, collecting a stack trace for every
new file descriptor adds overhead to fast path operations like open(),
dup(), and socket().

This patch adds a new configuration option CONFIG_FS_BACKTRACE_DEFAULT.
When enabled (default behavior), the GROUP_FLAG_FD_BACKTRACE flag is
automatically set during group allocation, causing backtrace to be
captured for all tasks globally, preserving the original diagnostic
capability.

When disabled, backtrace capture is zero-cost by default and must be
explicitly enabled per task group using GROUP_FLAG_FD_BACKTRACE.

Signed-off-by: zhanxiaoqi <zhanxiaoqi@bytedance.com>

fs/inode/inode.h

@@ -75,13 +75,22 @@
 #  define FS_ADD_BACKTRACE(fd) \
      do \
        { \
-          int n = sched_backtrace(_SCHED_GETTID(), \
-                                  (fd)->f_backtrace, \
-                                  CONFIG_FS_BACKTRACE, \
-                                  CONFIG_FS_BACKTRACE_SKIP); \
-          if (n < CONFIG_FS_BACKTRACE) \
+          FAR struct tcb_s *tcb = nxsched_get_tcb(nxsched_gettid()); \
+          if (tcb != NULL && tcb->group != NULL && \
+              (tcb->group->tg_flags & GROUP_FLAG_FD_BACKTRACE) != 0) \
             { \
-              (fd)->f_backtrace[n] = NULL; \
+              int n = sched_backtrace(tcb->pid, \
+                                      (fd)->f_backtrace, \
+                                      CONFIG_FS_BACKTRACE, \
+                                      CONFIG_FS_BACKTRACE_SKIP); \
+              if (n < CONFIG_FS_BACKTRACE) \
+                { \
+                  (fd)->f_backtrace[n] = NULL; \
+                } \
+            } \
+          else \
+            { \
+              (fd)->f_backtrace[0] = NULL; \
             } \
        } \
      while (0)

fs/vfs/Kconfig

@@ -99,3 +99,13 @@ config FS_BACKTRACE_SKIP
 	depends on FS_BACKTRACE > 0
 	---help---
 		Skip depth of backtrace.
+
+config FS_BACKTRACE_DEFAULT
+	bool "Enable the backtrace record by default"
+	default y
+	depends on FS_BACKTRACE > 0
+	---help---
+		Enable automatic backtrace capture for all file descriptor operations
+		globally. When disabled, backtrace capture is zero-cost by default
+		and must be explicitly enabled per task group by setting the
+		GROUP_FLAG_FD_BACKTRACE flag.

include/nuttx/sched.h

@@ -117,6 +117,7 @@
 #define GROUP_FLAG_PRIVILEGED      (1 << 1)                      /* Bit 1: Group is privileged */
 #define GROUP_FLAG_DELETED         (1 << 2)                      /* Bit 2: Group has been deleted but not yet freed */
 #define GROUP_FLAG_EXITING         (1 << 3)                      /* Bit 3: Group exit is in progress */
+#define GROUP_FLAG_FD_BACKTRACE    (1 << 4)                      /* Bit 4: Enable FD backtrace for the group */
                                                                  /* Bits 3-7: Available */
 
 /* Values for struct child_status_s ch_flags */

sched/group/group_create.c

@@ -163,6 +163,12 @@ int group_allocate(FAR struct tcb_s *tcb, uint8_t ttype)
   sq_init(&group->tg_members);
 #endif
 
+#ifdef CONFIG_FS_BACKTRACE_DEFAULT
+  /* Enable FD backtrace for the group by default */
+
+  group->tg_flags |= GROUP_FLAG_FD_BACKTRACE;
+#endif
+
   /* Attach the group to the TCB */
 
   tcb->group = group;