kernel/acct.c

Source file repositories/reference/linux-study-clean/kernel/acct.c

File Facts

System
Linux kernel
Corpus path
kernel/acct.c
Extension
.c
Size
16946 bytes
Lines
628
Domain
Core OS
Bucket
Scheduler, Processes, Timers, Sync, And Syscalls
Inferred role
Core OS: syscall or user/kernel boundary
Status
core implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

SYSCALL_DEFINE1(acct, const char __user *, name)
{
	int error = 0;

	if (!capable(CAP_SYS_PACCT))
		return -EPERM;

	if (name) {
		mutex_lock(&acct_on_mutex);
		error = acct_on(name);
		mutex_unlock(&acct_on_mutex);
	} else {
		rcu_read_lock();
		pin_kill(task_active_pid_ns(current)->bacct);
	}

	return error;
}

void acct_exit_ns(struct pid_namespace *ns)
{
	rcu_read_lock();
	pin_kill(ns->bacct);
}

/*
 *  encode an u64 into a comp_t
 *
 *  This routine has been adopted from the encode_comp_t() function in
 *  the kern_acct.c file of the FreeBSD operating system. The encoding
 *  is a 13-bit fraction with a 3-bit (base 8) exponent.
 */

#define	MANTSIZE	13			/* 13 bit mantissa. */
#define	EXPSIZE		3			/* Base 8 (3 bit) exponent. */
#define	MAXFRACT	((1 << MANTSIZE) - 1)	/* Maximum fractional value. */

static comp_t encode_comp_t(u64 value)
{
	int exp, rnd;

	exp = rnd = 0;
	while (value > MAXFRACT) {
		rnd = value & (1 << (EXPSIZE - 1));	/* Round up? */
		value >>= EXPSIZE;	/* Base 8 exponent == 3 bit shift. */
		exp++;
	}

	/*
	 * If we need to round up, do it (and handle overflow correctly).
	 */
	if (rnd && (++value > MAXFRACT)) {
		value >>= EXPSIZE;
		exp++;
	}

	if (exp > (((comp_t) ~0U) >> MANTSIZE))
		return (comp_t) ~0U;
	/*
	 * Clean it up and polish it off.
	 */
	exp <<= MANTSIZE;		/* Shift the exponent into place */
	exp += value;			/* and add on the mantissa. */
	return exp;
}

#if ACCT_VERSION == 1 || ACCT_VERSION == 2
/*
 * encode an u64 into a comp2_t (24 bits)
 *
 * Format: 5 bit base 2 exponent, 20 bits mantissa.
 * The leading bit of the mantissa is not stored, but implied for
 * non-zero exponents.
 * Largest encodable value is 50 bits.
 */

#define MANTSIZE2       20                      /* 20 bit mantissa. */
#define EXPSIZE2        5                       /* 5 bit base 2 exponent. */
#define MAXFRACT2       ((1ul << MANTSIZE2) - 1) /* Maximum fractional value. */
#define MAXEXP2         ((1 << EXPSIZE2) - 1)    /* Maximum exponent. */

static comp2_t encode_comp2_t(u64 value)
{
	int exp, rnd;

	exp = (value > (MAXFRACT2>>1));
	rnd = 0;
	while (value > MAXFRACT2) {
		rnd = value & 1;
		value >>= 1;

Annotation

Implementation Notes