Detailed description of IOCTL functions in Linux

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This function affects an open file referenced by the FD parameter.

# Include <unistd. h>

Int IOCTL (int fd, int request,.../* void * Arg */);

Return 0: Success-1: Error

The third parameter is always a pointer, but the pointer type depends on the request parameter.

We can divide network-related requests into 6 categories:

Set interface operations

File Operations

Interface operation

ARP high-speed cache operations

Route table operations

Stream System

The following table lists the Request Parameters for network-related IOCTL requests and the data types that the ARG address must point:

Category	Request	Description	Data Type
Set Connect Port	Siocatmark Siocspgrp Siocgpgrp	Whether it is in the out-of-band mark Set the process ID or process group ID of the Set Interface Obtain the process ID or group ID of the Set interface.	Int Int Int
Text Parts	Fionbin Fioasync Fionread Fiosetown Fiogetown	Set/clear non-blocking I/O flag Set/clear signal-driven asynchronous I/O flag Obtain the number of bytes in the receiving cache. Set the process ID or group ID of the file. Obtain the process ID or group ID of the file.	Int Int Int Int Int
Connect Port	Siocgifconf Siocsifaddr Siocgifaddr Siocsifflags Siocgifflags Siocsifdstaddr Siocgifdstaddr Siocgifbrdaddr Siocsifbrdaddr Siocgifnetmask Siocsifnetmask Siocgifmetric Siocsifmetric Siocgifmtu Siocxxx	Retrieve the list of all interfaces Set the interface address Obtain the interface address Set interface flag Get interface flag Set point-to-point address Get point-to-point address Get broadcast address Set broadcast address Obtain Subnet Mask Set Subnet Mask Obtain the measure of an interface Set the measure of the interface Obtain the MTU Interface (A lot more depends on the implementation of the system)	Struct ifconf Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq Struct ifreq
ARP	Siocsarp Siocgarp Siocdarp	Create/modify ARP table items Obtain ARP table items Delete ARP table items	Struct arpreq Struct arpreq Struct arpreq
Road By	Siocaddrt Siocdelrt	Add path Delete path	Struct rtentry Struct rtentry
Stream	I _xxx

Set operation:

There are three IOCTL requests explicitly used to set interface operations. Both require that the third parameter of IOCTL be a pointer to an integer.

Siocatmark: If the degree pointer of this set of interfaces is currently in the out-of-band mark, a non-0 value is returned through the integer pointed to by the third parameter; otherwise, a 0 value is returned. POSIX replaces this request with the sockatmark function.

Siocgpgrp: return the process ID or group ID of this interface through the integer indicated by the third parameter. This ID specifies the receiving process of the sigio or sigurg signal of this interface. This request is equivalent to the f_getown command of fcntl. POSIX standardizes the fcntl function.

Siocspgrp: sets the process ID or group ID of this interface to the integer pointed to by the third parameter. This ID specifies the receiving process of the sigio or sigurg signal of this interface, this request is equivalent to the f_setown command of fcntl. POSIX standardizes fcntl operations.

File Operations:

The following five requests require the third parameter of IOCTL to point to an integer.

Fionbio: Based on the third parameter of ioctl, point to a 0 or non-0 value to clear or set the non-blocking flag of this interface. This request is equivalent to the o_nonblock File status flag, which is cleared or set through the f_setfl command of fcntl.

Fioasync: Based on the third parameter of iocl, point to a 0 value or a non-0 value to clear or set the signal-driven asynchronous I/O flag for this interface, respectively, it determines whether to receive asynchronous I/O signals (sigio) for this interface ). This request is equivalent to the o_async File status flag, which can be cleared or set through the f_setfl command of fcntl.

Fionread: returns the number of bytes in the buffer zone currently received by this interface through the integer pointed to by the third parameter of IOCTL. This feature is also applicable to files, pipelines, and terminals.

Fiosetown: equivalent to siocspgrp for the set interface.

Fiogetown: equivalent to siocgpgrp for the set interface.

Interface Configuration:

All the interfaces in the system are completed by the siocgifconf request. The request uses the ifconf structure, and the ifconf uses the ifreq

Structure:

Struct ifconf {

Int ifc_len; // buffer size

Union {

Caddr_t ifcu_buf; // input from user-> kernel

Struct ifreq * ifcu_req; // return of structures returned

} Ifc_ifcu;

};

# Define ifc_buf ifc_ifcu.ifcu_buf // buffer address

# Define ifc_req ifc_ifcu.ifcu_req // array of structures returned

# Define ifnamsiz 16

Struct ifreq {

Char ifr_name [ifnamsiz]; // Interface Name, e.g., "le0"

Union {

Struct sockaddr ifru_addr;

Struct sockaddr ifru_dstaddr;

Struct sockaddr ifru_broadaddr;

Short ifru_flags;

Int ifru_metric;

Caddr_t ifru_data;

} Ifr_ifru;

};

# Define ifr_addr ifr_ifru.ifru_addr // address

# Define ifr_dstaddr ifr_ifru.ifru_dstaddr // otner end of p-to-P Link

# Define ifr_broadaddr ifr_ifru.ifru_broadaddr // broadcast address

# Define ifr_flags ifr_ifru.ifru_flags // flags

# Define ifr_metric ifr_ifru.ifru_metric // Metric

# Define ifr_data ifr_ifru.ifru_data // for use by Interface

Before calling ioctl, we must first split a buffer zone and an ifconf structure before initializing the latter. For example

Shows the initialization structure of an ifconf structure, where the buffer size is 1024, and the third parameter of IOCTL points

Such an ifconf structure.

Ifc_len

Ifc_buf

1024

---------------------> Cache

Assume that the kernel returns two ifreq structures. When IOCTL returns, the two ifreq structures are entered in the buffer zone of the same ifconf structure. The ifc_len members of the ifconf structure are also updated, to reflect the amount of information stored in the buffer

Generally, the call of IOCTL in a user program is: IOCTL (int fd, int command, (char *) argstruct) IOCTL call is related to network programming (this article only discusses this ), the file descriptor FD is actually returned by the socket () System Call. The value of the command parameter is specified by/usr/include/Linux/sockios. h. Different functions of these commands can be divided into the following sub-classes:
• Change the route table (for example, siocaddrt and siocdelrt ),
• Read/update arp/RARP caches (for example, siocdarp and siocsrarp ),
• Generally related to network interfaces (such as siocgifname and siocsifaddr)
There are various examples in the gooodies directory that show how to use IOCTL. When you look at these programs, note that the argstruct parameter is related to the command parameter. For example, IOCTL related to the route table uses the rtentry structure. rtentry is defined in/usr/include/Linux/route. H (see the example adddefault. C ). ARP-related IOCTL calls use the arpreq structure. arpreq is defined in/usr/include/Linux/if_arp.h (see the example of arpread. c) The command parameter used for IOCTL calls related to network interfaces usually looks in the form of siocxifyyyy. Here, X is either S (set, write) or G (get, read ). In the getifinfo. C program, command parameters in this form are used to read IP addresses, hardware addresses, broadcast addresses, and flag related to network interfaces ). In these IOCTL calls, the third parameter is the ifreq structure, which is defined in/usr/include/Linux/If. h. In some cases, ioctrl calls may use new definitions other than sockios. H. For example, the wavelan wireless network card