um: Add kerneldoc for userspace_tramp() and start_userspace() (e9099830) · Commits · 戴 / test

arch/um/os-Linux/skas/process.c

+30 −1

Original line number	Diff line number	Diff line
		@@ -108,7 +108,7 @@ static void get_skas_faultinfo(int pid, struct faultinfo *fi)
		wait_stub_done(pid);

		/*
		* faultinfo is prepared by the stub-segv-handler at start of
		* faultinfo is prepared by the stub_segv_handler at start of
		* the stub stack page. We just have to copy it.
		*/
		memcpy(fi, (void )current_stub_stack(), sizeof(fi));
		@@ -175,6 +175,21 @@ static void handle_trap(int pid, struct uml_pt_regs *regs,

		extern char __syscall_stub_start[];

		/**
		* userspace_tramp() - userspace trampoline
		* @stack: pointer to the new userspace stack page, can be NULL, if? FIXME:
		*
		* The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
		* This function will run on a temporary stack page.
		* It ptrace()'es itself, then
		* Two pages are mapped into the userspace address space:
		* - STUB_CODE (with EXEC), which contains the skas stub code
		* - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel.
		* Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
		* And last the process stops itself to give control to the UML kernel for this userspace process.
		*
		* Return: Always zero, otherwise the current userspace process is ended with non null exit() call
		*/
		static int userspace_tramp(void *stack)
		{
		void *addr;
		@@ -236,12 +251,24 @@ static int userspace_tramp(void *stack)

		int userspace_pid[NR_CPUS];

		/**
		* start_userspace() - prepare a new userspace process
		* @stub_stack: pointer to the stub stack. Can be NULL, if? FIXME:
		*
		* Setups a new temporary stack page that is used while userspace_tramp() runs
		* Clones the kernel process into a new userspace process, with FDs only.
		*
		* Return: When positive: the process id of the new userspace process,
		* when negative: an error number.
		* FIXME: can PIDs become negative?!
		*/
		int start_userspace(unsigned long stub_stack)
		{
		void *stack;
		unsigned long sp;
		int pid, status, n, flags, err;

		/* setup a temporary stack page */
		stack = mmap(NULL, UM_KERN_PAGE_SIZE,
		PROT_READ \| PROT_WRITE \| PROT_EXEC,
		MAP_PRIVATE \| MAP_ANONYMOUS, -1, 0);
		@@ -252,10 +279,12 @@ int start_userspace(unsigned long stub_stack)
		return err;
		}

		/* set stack pointer to the end of the stack page, so it can grow downwards */
		sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);

		flags = CLONE_FILES \| SIGCHLD;

		/* clone into new userspace process */
		pid = clone(userspace_tramp, (void ) sp, flags, (void ) stub_stack);
		if (pid < 0) {
		err = -errno;

Admin message