root/include/linux/task_io_accounting.h

INCLUDED FROM

/*
 * task_io_accounting: a structure which is used for recording a single task's
 * IO statistics.
 *
 * Don't include this header file directly - it is designed to be dragged in via
 * sched.h.
 *
 * Blame akpm@osdl.org for all this.
 */

struct task_io_accounting {
#ifdef CONFIG_TASK_XACCT
        /* bytes read */
        u64 rchar;
        /*  bytes written */
        u64 wchar;
        /* # of read syscalls */
        u64 syscr;
        /* # of write syscalls */
        u64 syscw;
#endif /* CONFIG_TASK_XACCT */

#ifdef CONFIG_TASK_IO_ACCOUNTING
        /*
         * The number of bytes which this task has caused to be read from
         * storage.
         */
        u64 read_bytes;

        /*
         * The number of bytes which this task has caused, or shall cause to be
         * written to disk.
         */
        u64 write_bytes;

        /*
         * A task can cause "negative" IO too.  If this task truncates some
         * dirty pagecache, some IO which another task has been accounted for
         * (in its write_bytes) will not be happening.  We _could_ just
         * subtract that from the truncating task's write_bytes, but there is
         * information loss in doing that.
         */
        u64 cancelled_write_bytes;
#endif /* CONFIG_TASK_IO_ACCOUNTING */
};