user_regset_active_fn(9) [suse man page]

USER_REGSET_ACTIVE_F(9) 					   Machine State					   USER_REGSET_ACTIVE_F(9)

NAME

       user_regset_active_fn - type of active function in struct user_regset

SYNOPSIS

       typedef int user_regset_active_fn(struct task_struct * target, const struct user_regset * regset);

ARGUMENTS

       target
	   thread being examined

       regset
	   regset being examined

DESCRIPTION

       Return -ENODEV if not available on the hardware found. Return 0 if no interesting state in this thread. Return >0 number of size units of
       interesting state. Any get call fetching state beyond that number will see the default initialization state for this data, so a caller that
       knows what the default state is need not copy it all out. This call is optional; the pointer is NULL if there is no inexpensive check to
       yield a value < n.

Kernel Hackers Manual 2.6.					     July 2010						   USER_REGSET_ACTIVE_F(9)

STRUCT 
USER_REGSET(9)						   Machine State					     STRUCT USER_REGSET(9)

NAME

       struct_user_regset - accessible thread CPU state

SYNOPSIS

       struct user_regset {
	 user_regset_get_fn * get;
	 user_regset_set_fn * set;
	 user_regset_active_fn * active;
	 user_regset_writeback_fn * writeback;
	 unsigned int n;
	 unsigned int size;
	 unsigned int align;
	 unsigned int bias;
	 unsigned int core_note_type;
       };

MEMBERS

       get
	   Function to fetch values.

       set
	   Function to store values.

       active
	   Function to report if regset is active, or NULL.

       writeback
	   Function to write data back to user memory, or NULL.

       n
	   Number of slots (registers).

       size
	   Size in bytes of a slot (register).

       align
	   Required alignment, in bytes.

       bias
	   Bias from natural indexing.

       core_note_type
	   ELF note n_type value used in core dumps.

DESCRIPTION

       This data structure describes a machine resource we call a register set. This is part of the state of an individual thread, not necessarily
       actual CPU registers per se. A register set consists of a number of similar slots, given by n. Each slot is size bytes, and aligned to
       align bytes (which is at least size).

       These functions must be called only on the current thread or on a thread that is in TASK_STOPPED or TASK_TRACED state, that we are
       guaranteed will not be woken up and return to user mode, and that we have called wait_task_inactive on. (The target thread always might
       wake up for SIGKILL while these functions are working, in which case that thread's user_regset state might be scrambled.)

       The pos argument must be aligned according to align; the count argument must be a multiple of size. These functions are not responsible for
       checking for invalid arguments.

       When there is a natural value to use as an index, bias gives the difference between the natural index and the slot index for the register
       set. For example, x86 GDT segment descriptors form a regset; the segment selector produces a natural index, but only a subset of that index
       space is available as a regset (the TLS slots); subtracting bias from a segment selector index value computes the regset slot.

       If nonzero, core_note_type gives the n_type field (NT_* value) of the core file note in which this regset's data appears. NT_PRSTATUS is a
       special case in that the regset data starts at offsetof(struct elf_prstatus, pr_reg) into the note data; that is part of the per-machine
       ELF formats userland knows about. In other cases, the core file note contains exactly the whole regset (n * size) and nothing else. The
       core file note is normally omitted when there is an active function and it returns zero.

Kernel Hackers Manual 2.6.					     July 2010						     STRUCT USER_REGSET(9)