Copyright (c) 2007 Robert N. M. Watson
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$FreeBSD: releng/11.0/lib/libc/net/ethers.3 224701 2011-08-08 03:09:03Z hrs $
.Dd October 30, 2007 .Dt ETHERS 3 .Os .Sh NAME .Nm ethers , .Nm ether_line , .Nm ether_aton , .Nm ether_aton_r , .Nm ether_ntoa , .Nm ether_ntoa_r , .Nm ether_ntohost , .Nm ether_hostton .Nd Ethernet address conversion and lookup routines .Sh LIBRARY .Lb libc .Sh SYNOPSIS n sys/types.h n sys/socket.h n net/ethernet.h .Ft int .Fn ether_line "const char *l" "struct ether_addr *e" "char *hostname" .Ft struct ether_addr * .Fn ether_aton "const char *a" .Ft struct ether_addr * .Fn ether_aton_r "const char *a" "struct ether_addr *e" .Ft char * .Fn ether_ntoa "const struct ether_addr *n" .Ft char * .Fn ether_ntoa_r "const struct ether_addr *n" "char *buf" .Ft int .Fn ether_ntohost "char *hostname" "const struct ether_addr *e" .Ft int .Fn ether_hostton "const char *hostname" "struct ether_addr *e" .Sh DESCRIPTION These functions operate on ethernet addresses using an .Vt ether_addr structure, which is defined in the header file n net/ethernet.h : d -literal -offset indent /* * The number of bytes in an ethernet (MAC) address. */ #define ETHER_ADDR_LEN 6 /* * Structure of a 48-bit Ethernet address. */ struct ether_addr { u_char octet[ETHER_ADDR_LEN]; }; .Ed
p The function .Fn ether_line scans .Fa l , an .Tn ASCII string in .Xr ethers 5 format and sets .Fa e to the ethernet address specified in the string and .Fa h to the hostname. This function is used to parse lines from
a /etc/ethers into their component parts.
p The .Fn ether_aton and .Fn ether_aton_r functions convert .Tn ASCII representation of ethernet addresses into .Vt ether_addr structures. Likewise, the .Fn ether_ntoa and .Fn ether_ntoa_r functions convert ethernet addresses specified as .Vt ether_addr structures into .Tn ASCII strings.
p The .Fn ether_ntohost and .Fn ether_hostton functions map ethernet addresses to their corresponding hostnames as specified in the
a /etc/ethers database. The .Fn ether_ntohost function converts from ethernet address to hostname, and .Fn ether_hostton converts from hostname to ethernet address. .Sh RETURN VALUES The .Fn ether_line function returns zero on success and non-zero if it was unable to parse any part of the supplied line .Fa l . It returns the extracted ethernet address in the supplied .Vt ether_addr structure .Fa e and the hostname in the supplied string .Fa h .
p On success, .Fn ether_ntoa and .Fn ether_ntoa_r functions return a pointer to a string containing an .Tn ASCII representation of an ethernet address. If it is unable to convert the supplied .Vt ether_addr structure, it returns a .Dv NULL pointer. .Fn ether_ntoa stores the result in a static buffer; .Fn ether_ntoa_r stores the result in a user-passed buffer.
p Likewise, .Fn ether_aton and .Fn ether_aton_r return a pointer to an .Vt ether_addr structure on success and a .Dv NULL pointer on failure. .Fn ether_aton stores the result in a static buffer; .Fn ether_aton_r stores the result in a user-passed buffer.
p The .Fn ether_ntohost and .Fn ether_hostton functions both return zero on success or non-zero if they were unable to find a match in the
a /etc/ethers database. .Sh NOTES The user must ensure that the hostname strings passed to the .Fn ether_line , .Fn ether_ntohost and .Fn ether_hostton functions are large enough to contain the returned hostnames. .Sh NIS INTERACTION If the
a /etc/ethers contains a line with a single + in it, the .Fn ether_ntohost and .Fn ether_hostton functions will attempt to consult the NIS
a ethers.byname and
a ethers.byaddr maps in addition to the data in the
a /etc/ethers file. .Sh SEE ALSO .Xr ethers 5 , .Xr yp 8 .Sh HISTORY This particular implementation of the .Nm library functions were written for and first appeared in .Fx 2.1 . Thread-safe function variants first appeared in .Fx 7.0 . .Sh BUGS The .Fn ether_aton and .Fn ether_ntoa functions returns values that are stored in static memory areas which may be overwritten the next time they are called.
p .Fn ether_ntoa_r accepts a character buffer pointer, but not a buffer length. The caller must ensure adequate space is available in the buffer in order to avoid a buffer overflow.