Python：错误：（9，“错误的文件描述符”）

Question

I have error at:

"File "/home/pi/blescan.py", line 78, in hci_le_set_scan_parameters
    old_filter = sock.getsockopt( bluez.SOL_HCI, bluez.HCI_FILTER, 14)

error: (9, 'Bad file descriptor')"

I am unsure what is the cause of the error, and I have tried whatever solution that is available online, but it resulted in the same error.

DEBUG = False

import os
import sys
import struct
import bluetooth._bluetooth as bluez
from time import gmtime, strftime


LE_META_EVENT = 0x3e
LE_PUBLIC_ADDRESS=0x00
LE_RANDOM_ADDRESS=0x01
LE_SET_SCAN_PARAMETERS_CP_SIZE=7
OGF_LE_CTL=0x08
OCF_LE_SET_SCAN_PARAMETERS=0x000B
OCF_LE_SET_SCAN_ENABLE=0x000C
OCF_LE_CREATE_CONN=0x000D

LE_ROLE_MASTER = 0x00
LE_ROLE_SLAVE = 0x01

# these are actually subevents of LE_META_EVENT
EVT_LE_CONN_COMPLETE=0x01
EVT_LE_ADVERTISING_REPORT=0x02
EVT_LE_CONN_UPDATE_COMPLETE=0x03
EVT_LE_READ_REMOTE_USED_FEATURES_COMPLETE=0x04

# Advertisment event types
ADV_IND=0x00
ADV_DIRECT_IND=0x01
ADV_SCAN_IND=0x02
ADV_NONCONN_IND=0x03
ADV_SCAN_RSP=0x04


def returnnumberpacket(pkt):
    myInteger = 0
    multiple = 256
    for c in pkt:
        myInteger +=  struct.unpack("B",c)[0] * multiple
        multiple = 1
    return myInteger 

def returnstringpacket(pkt):
    myString = "";
    for c in pkt:
        myString +=  "%02x" %struct.unpack("B",c)[0]
    return myString 

def printpacket(pkt):
    for c in pkt:
        sys.stdout.write("%02x " % struct.unpack("B",c)[0])

def get_packed_bdaddr(bdaddr_string):
    packable_addr = []
    addr = bdaddr_string.split(':')
    addr.reverse()
    for b in addr: 
        packable_addr.append(int(b, 16))
    return struct.pack("<BBBBBB", *packable_addr)

def packed_bdaddr_to_string(bdaddr_packed):
    return ':'.join('%02x'%i for i in struct.unpack("<BBBBBB",bdaddr_packed[::-1]))

def hci_enable_le_scan(sock):
    hci_toggle_le_scan(sock, 0x01)

def hci_disable_le_scan(sock):
    hci_toggle_le_scan(sock, 0x00)

def hci_toggle_le_scan(sock, enable):
    cmd_pkt = struct.pack("<BB", enable, 0x00)
    bluez.hci_send_cmd(sock, OGF_LE_CTL, OCF_LE_SET_SCAN_ENABLE, cmd_pkt)


def hci_le_set_scan_parameters(sock):
    old_filter = sock.getsockopt( bluez.SOL_HCI, bluez.HCI_FILTER, 14)



    SCAN_RANDOM = 0x01
    OWN_TYPE = SCAN_RANDOM
    SCAN_TYPE = 0x01


def parse_events(sock, loop_count=100):
    old_filter = sock.getsockopt( bluez.SOL_HCI, bluez.HCI_FILTER, 14)

    CurrentTime = strftime("%H:%M,%S", gmtime())
    flt = bluez.hci_filter_new()
    bluez.hci_filter_all_events(flt)
    bluez.hci_filter_set_ptype(flt, bluez.HCI_EVENT_PKT)
    sock.setsockopt( bluez.SOL_HCI, bluez.HCI_FILTER, flt )
    done = False
    results = []
    myFullList = []
    for i in range(0, loop_count):
        pkt = sock.recv(255)
        ptype, event, plen = struct.unpack("BBB", pkt[:3])
        #print "--------------" 
        if event == bluez.EVT_INQUIRY_RESULT_WITH_RSSI:
                i =0
        elif event == bluez.EVT_NUM_COMP_PKTS:
                i =0 
        elif event == bluez.EVT_DISCONN_COMPLETE:
                i =0 
        elif event == LE_META_EVENT:
            subevent, = struct.unpack("B", pkt[3])
            pkt = pkt[4:]
            if subevent == EVT_LE_CONN_COMPLETE:
                le_handle_connection_complete(pkt)
            elif subevent == EVT_LE_ADVERTISING_REPORT:
                #print "advertising report"
                num_reports = struct.unpack("B", pkt[0])[0]
                report_pkt_offset = 0
                for i in range(0, num_reports):

                    if (DEBUS == True):
                        print "-------------"
                        print "\tMAC address: ",        packed_bdaddr_to_string(pkt[report_pkt_offset + 3:report_pkt_offset + 9])
                        TxPower, = struct.unpack("b",  pkt[report_pkt_offset -2])
                        print "\tTxpower:", -TxPower
                        rssi, = struct.unpack("b", pkt[report_pkt_offset -1])
                        print "\tRSSI:", rssi
                        print "\tTime:", CurrentTime
                    # build the return string
                    Adstring = packed_bdaddr_to_string(pkt[report_pkt_offset + 3:report_pkt_offset + 9])
                    Adstring += ","
                    Adstring += returnstringpacket(pkt[report_pkt_offset -22: report_pkt_offset - 6])
                    Adstring += ","
                    Adstring += "%i" % returnnumberpacket(pkt[report_pkt_offset -6: report_pkt_offset - 4])
                    Adstring += ","
                    Adstring += "%i" % returnnumberpacket(pkt[report_pkt_offset -4: report_pkt_offset - 2])
                    Adstring += ","
                    Adstring += "%i" % struct.unpack("b", pkt[report_pkt_offset -2])
                    Adstring += ","
                    Adstring += "%i" % struct.unpack("b", pkt[report_pkt_offset -1])
                    #print "\tAdstring=", Adstring
                    myFullList.append(Adstring)
                done = True
    sock.setsockopt( bluez.SOL_HCI, bluez.HCI_FILTER, old_filter )
    return myFullList

Full Traceback error:

Traceback (most recent call last):
  File "/home/pi/blescan.py", line 79, in hci_le_set_scan_parameters
    old_filter = socket.getsockopt( bluez.SOL_HCI, bluez.HCI_FILTER, 14)
error: (9, 'Bad file descriptor')

Traceback (most recent call last):
  File "/home/pi/testblescan.py", line 15, in <module>
    blescan.hci_enable_le_scan(socket)
  File "/home/pi/blescan.py", line 67, in hci_enable_le_scan
    hci_toggle_le_scan(socket, 0x01)
  File "/home/pi/blescan.py", line 74, in hci_toggle_le_scan
    bluez.hci_send_cmd(socket, OGF_LE_CTL, OCF_LE_SET_SCAN_ENABLE, cmd_pkt)
error: (9, 'Bad file descriptor')

Answer 1

The output appears to be reporting an OSError, which is accompanied by an error code. This isn't a Python-specific problem, because it is being raised by the underlying operating system.

You can use the standard library's errno feature to get information about the operating system's error codes.

You can also ask for the description of an error code via the os.strerror function :

import os

os.strerror(9)   # Returns the text value “Bad file descriptor”.

So, something your program is doing makes use of a file descriptor (the integer that represents an input/output stream in the running program) that doesn't actually have a file attached. The operating system complains, and Python reports that as an OSError.

You can interrogate the OSError object you catch for its error code (the errno attribute) and what filename was reported (the filename attribute):

try:
    do_the_thing()
except OSError as exc:
    logger_for_this_program(
            "Got OSError (code {exc.errno:d}, filename {exc.filename})".format(
                exc=exc))