函数buf_read_page

/********************************************************************//**
High-level function which reads a page asynchronously from a file to the
buffer buf_pool if it is not already there. Sets the io_fix flag and sets
an exclusive lock on the buffer frame. The flag is cleared and the x-lock
released by the i/o-handler thread.
@return TRUE if page has been read in, FALSE in case of failure */
UNIV_INTERN
ibool
buf_read_page(
/*==========*/
    ulint    space,    /*!< in: space id */
    ulint    zip_size,/*!< in: compressed page size in bytes, or 0 */
    ulint    offset)    /*!< in: page number */
{
    buf_pool_t*    buf_pool = buf_pool_get(space, offset);
    ib_int64_t    tablespace_version;
    ulint        count;
    ulint        err;

    tablespace_version = fil_space_get_version(space);

    /* We do the i/o in the synchronous aio mode to save thread
    switches: hence TRUE */
    //详见
    count = buf_read_page_low(&err, TRUE, BUF_READ_ANY_PAGE, space,zip_size, FALSE,tablespace_version, offset);
    srv_buf_pool_reads += count;
    if (err == DB_TABLESPACE_DELETED) {
        ut_print_timestamp(stderr);
        fprintf(stderr,
            "  InnoDB: Error: trying to access"
            " tablespace %lu page no. %lu,\n"
            "InnoDB: but the tablespace does not exist"
            " or is just being dropped.\n",
            (ulong) space, (ulong) offset);
    }

    /* Flush pages from the end of the LRU list if necessary */
    buf_flush_free_margin(buf_pool);

    /* Increment number of I/O operations used for LRU policy. */
    buf_LRU_stat_inc_io();

    );
}