1 files changed, 46 insertions, 5 deletions

diff --git a/lib/libc/sys/fcntl.2 b/lib/libc/sys/fcntl.2
index f53c02f2403d..5587bcfba35c 100644
--- a/lib/libc/sys/fcntl.2
+++ b/lib/libc/sys/fcntl.2
@@ -128,9 +128,9 @@ flags are as follows:
 .Bl -tag -width O_NONBLOCKX
 .It Dv O_NONBLOCK
 Non-blocking I/O; if no data is available to a
-.Xr read
+.Xr read 2
 call, or if a
-.Xr write
+.Xr write 2
 operation would block,
 the read or write call returns -1 with the error
 .Er EAGAIN .
@@ -295,10 +295,10 @@ This semantic means that applications must be aware of any files that
 a subroutine library may access.
 For example if an application for updating the password file locks the
 password file database while making the update, and then calls
-.Xr getpwname 3
+.Xr getpwnam 3
 to retrieve a record,
 the lock will be lost because 
-.Xr getpwname 3
+.Xr getpwnam 3
 opens, reads, and closes the password database.
 The database close will release all locks that the process has
 associated with the database, even if the library routine never
@@ -330,6 +330,29 @@ This implementation detects that sleeping until a locked region is unlocked
 would cause a deadlock and fails with an
 .Er EDEADLK
 error.
+.Sh IMPLEMENTATION NOTES
+.Pp
+In the non-threaded library
+.Fn fcntl
+is implemented as the
+.Va fcntl
+syscall.
+.Pp
+In the threaded library, the
+.Va fcntl
+syscall is assembled to
+.Fn _thread_sys_fcntl
+and
+.Fn fcntl
+is implemented as a function which disables thread rescheduling, locks
+.Va fd
+for read and write, then calls
+.Fn _thread_sys_fcntl .
+Before returning,
+.Fn fcntl
+unlocks
+.Va fd
+and enables thread rescheduling.
 .Sh RETURN VALUES
 Upon successful completion, the value returned depends on
 .Fa cmd
@@ -467,13 +490,31 @@ is
 and
 the process ID given as argument is not in use.
 .El
+.Pp
+In addition, if 
+.Fa fd
+refers to a descriptor open on a terminal device (as opposed to a
+descriptor open on a socket), a
+.Fa cmd
+of
+.Dv F_SETOWN
+can fail for the same reasons as in
+.Xr tcsetpgrp 3 ,
+and a
+.Fa cmd
+of
+.Dv F_GETOWN
+for the reasons as stated in
+.Xr tcgetpgrp 3 .
 .Sh SEE ALSO
 .Xr close 2 ,
 .Xr execve 2 ,
 .Xr flock 2 ,
 .Xr getdtablesize 2 ,
 .Xr open 2 ,
-.Xr sigvec 2
+.Xr sigvec 2 ,
+.Xr tcgetpgrp 3 ,
+.Xr tcsetpgrp 3
 .Sh HISTORY
 The
 .Nm