Xlib â C Language X Interface

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Xlib − C LibraryX11, Release 6.7 DRAFT• Change, enable, or disable accessXdoes not provide any protection on a per-window basis. If you find out the resource ID of aresource, you can manipulate it. To provide some minimal level ofprotection, however, connectionsare permitted only from machines you trust. This is adequate on single-user workstationsbut obviously breaks down on timesharing machines. Although provisions exist in the X protocolfor proper connection authentication, the lack of a standard authentication server leaves host-levelaccess control as the only common mechanism.The initial set of hosts allowed to open connections typically consists of:• The host the window system is running on.• OnPOSIX-conformant systems, each host listed in the /etc/X?.hosts file. The ?indicatesthe number of the display. This file should consist of host names separated by newlines.DECnet nodes must terminate in :: to distinguish them from Internet hosts.If a host is not in the access control list when the access control mechanism is enabled and if thehost attempts to establish a connection, the server refuses the connection. To change the accesslist, the client must reside on the same host as the server and/or must have been granted permissionin the initial authorization at connection setup.Servers also can implement other access control policies in addition to or in place of this hostaccess facility. For further information about other access control implementations, see ‘‘X WindowSystem Protocol.’’9.8.1. Adding, Getting, or Removing HostsXlib provides functions that you can use to add, get, or remove hosts from the access control list.All the host access control functions use the XHostAddress structure, which contains:typedef struct {int family; /* for example FamilyInternet */int length; /* length of address, in bytes */char *address; /* pointer to where to find the address */}XHostAddress;The family member specifies which protocol address family to use (for example, TCP/IP or DECnet)and can be FamilyInternet, FamilyInternet6, FamilyDECnet, or FamilyChaos. Thelength member specifies the length of the address in bytes. The address member specifies apointer to the address.For TCP/IP, the address should be in network byte order. For IP version 4 addresses, the familyshould be FamilyInternet and the length should be 4 bytes. For IPversion 6 addresses, the familyshould be FamilyInternet6 and the length should be 16 bytes.For the DECnet family, the server performs no automatic swapping on the address bytes. APhaseIV address is 2 bytes long. The first byte contains the least significant 8 bits of the node number.The second byte contains the most significant 2 bits of the node number in the least significant 2bits of the byte and the area in the most significant 6 bits of the byte.To add a single host, use XAddHost.193
Xlib − C LibraryX11, Release 6.7 DRAFTXAddHost (display, host)Display *display;XHostAddress *host;displayhostSpecifies the connection to the X server.Specifies the host that is to be added.The XAddHost function adds the specified host to the access control list for that display. Theserver must be on the same host as the client issuing the command, or a BadAccess error results.XAddHost can generate BadAccess and BadValue errors.To add multiple hosts at one time, use XAddHosts.XAddHosts (display, hosts, num_hosts)Display *display;XHostAddress *hosts;int num_hosts;displayhostsnum_hostsSpecifies the connection to the X server.Specifies each host that is to be added.Specifies the number of hosts.The XAddHosts function adds each specified host to the access control list for that display. Theserver must be on the same host as the client issuing the command, or a BadAccess error results.XAddHosts can generate BadAccess and BadValue errors.To obtain a host list, use XListHosts.XHostAddress *XListHosts(display, nhosts_return, state_return)Display *display;int *nhosts_return;Bool *state_return;displaynhosts_returnstate_returnSpecifies the connection to the X server.Returns the number of hosts currently in the access control list.Returns the state of the access control.The XListHosts function returns the current access control list as well as whether the use of thelist at connection setup was enabled or disabled. XListHosts allows a program to find out whatmachines can make connections. It also returns a pointer to a list of host structures that were allocatedby the function. When no longer needed, this memory should be freed by calling XFree.To remove a single host, use XRemoveHost.194
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AcknowledgmentsThe design and imple
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Release 6Stephen Gildea (X Consorti
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Xlib − C LibraryX11, Release 6.7
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4.2. Translating Screen Coordinates
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10.7. Input Focus Events . . . . .
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13.5.6.1. Input Style . . . . . . .
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