diff options
Diffstat (limited to 'lib/libc')
| -rw-r--r-- | lib/libc/sys/select.2 | 55 |
1 files changed, 5 insertions, 50 deletions
diff --git a/lib/libc/sys/select.2 b/lib/libc/sys/select.2 index a0fa300fd3b..3dc9d35af9a 100644 --- a/lib/libc/sys/select.2 +++ b/lib/libc/sys/select.2 @@ -1,4 +1,4 @@ -.\" $OpenBSD: select.2,v 1.44 2021/11/16 13:46:16 visa Exp $ +.\" $OpenBSD: select.2,v 1.45 2022/01/21 16:18:16 deraadt Exp $ .\" $NetBSD: select.2,v 1.5 1995/06/27 22:32:28 cgd Exp $ .\" .\" Copyright (c) 1983, 1991, 1993 @@ -30,7 +30,7 @@ .\" .\" @(#)select.2 8.2 (Berkeley) 3/25/94 .\" -.Dd $Mdocdate: November 16 2021 $ +.Dd $Mdocdate: January 21 2022 $ .Dt SELECT 2 .Os .Sh NAME @@ -223,55 +223,10 @@ Although the provision of was intended to allow user programs to be written independent of the kernel limit on the number of open files, the dimension of a sufficiently large bit field for select remains a problem. -The default bit size of -.Ft fd_set -is based on the symbol -.Dv FD_SETSIZE -(currently 1024), -but that is somewhat smaller than the current kernel limit -to the number of open files. -However, in order to accommodate programs which might potentially -use a larger number of open files with select, it is possible -to increase this size within a program by providing -a larger definition of -.Dv FD_SETSIZE -before the inclusion of any headers. -The kernel will cope, and the userland libraries provided with the -system are also ready for large numbers of file descriptors. -.Pp -Alternatively, to be really safe, it is possible to allocate -.Ft fd_set -bit-arrays dynamically. -The idea is to permit a program to work properly even if it is -.Xr execve 2 Ns 'd -with 4000 file descriptors pre-allocated. -The following illustrates the technique which is used by -userland libraries: -.Bd -literal -offset indent -fd_set *fdsr; -int max = fd; - -fdsr = calloc(howmany(max+1, NFDBITS), sizeof(fd_mask)); -if (fdsr == NULL) { - ... - return (-1); -} -FD_SET(fd, fdsr); -n = select(max+1, fdsr, NULL, NULL, &tv); -\&... -free(fdsr); -.Ed -.Pp -Alternatively, it is possible to use the -.Xr poll 2 -interface. +If descriptor values greater than FD_SETSIZE are possible in +a program, use .Xr poll 2 -is more efficient when the size of -.Fn select Ns 's -.Ft fd_set -bit-arrays are very large, and for fixed numbers of -file descriptors one need not size and dynamically allocate a -memory object. +instead. .Pp .Fn select should probably have been designed to return the time remaining from the |