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Document O_NOCTTY and O_SYNC. O_NOCTTY is a nop on freebsd, while on

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other systems it prevents a tty from becoming a controlling tty on the
open.  O_SYNC is the POSIX name for O_FSYNC.

The Markup Police may need to tweak my references to standards.
This commit is contained in:
Warner Losh 2005-12-01 17:54:33 +00:00
parent ef8d441925
commit edd94d735c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=152989
1 changed files with 17 additions and 0 deletions
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17
lib/libc/sys/open.2
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@ -86,7 +86,9 @@ O_SHLOCK atomically obtain a shared lock
O_EXLOCK atomically obtain an exclusive lock
O_DIRECT eliminate or reduce cache effects
O_FSYNC synchronous writes
O_SYNC synchronous writes
O_NOFOLLOW do not follow symlinks
O_NOCTTY don't assign controlling terminal
.Ed
.Pp
Opening a file with
@ -133,6 +135,11 @@ the kernel will not cache written data
and all writes on the descriptor will not return until
the data to be written completes.
.Pp
.Dv O_SYNC
is a synonym for
.Dv O_FSYNC
required by POSIX.
.Pp
If
.Dv O_NOFOLLOW
is used in the mask and the target file passed to
@ -160,6 +167,16 @@ If it cannot avoid caching the data,
it will minimize the impact the data has on the cache.
Use of this flag can drastically reduce performance if not used with care.
.Pp
.Dv O_NOCTTY
may be used to ensure the OS does not assign this file as the
controlling terminal when it opens a tty device.
This is the default on
.Fx ,
but is present for POSIX 1003.1 compatibility.
.Fn open
will not assign controlling terminals on
.Fx .
.Pp
If successful,
.Fn open
returns a non-negative integer, termed a file descriptor.