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kern_poll: Restore explanatory comment removed in r177374

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The comment isn't stale.  The check is bogus in the sense that poll(2)
does not require pollfd entries to be unique in fd space, so there is no
reason there cannot be more pollfd entries than open or even allowed
fds.  The check is mostly a seatbelt against accidental misuse or
abuse.  FD_SETSIZE, while usually unrelated to poll, is used as an
arbitrary floor for systems with very low kern.maxfilesperproc.

Additionally, document this possible EINVAL condition in the poll.2
manual.

No functional change.

Reviewed by:	markj
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D17671
This commit is contained in:
Conrad Meyer 2018-11-01 23:46:23 +00:00
parent 209fcf8ed9
commit 78c2a9806e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=340038
2 changed files with 17 additions and 2 deletions
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12
lib/libc/sys/poll.2
View File

@ -28,7 +28,7 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd November 13, 2014
.Dd November 1, 2018
.Dt POLL 2
.Os
.Sh NAME
@ -232,7 +232,15 @@ points outside the process's allocated address space.
A signal was delivered before the time limit expired and
before any of the selected events occurred.
.It Bq Er EINVAL
The specified time limit is invalid. One of its components is negative or too large.
The specified time limit is invalid.
One of its components is negative or too large.
.It Bq Er EINVAL
The number of pollfd structures specified by
.Fa nfds
exceeds the system tunable
.Va kern.maxfilesperproc
and
.Dv FD_SETSIZE .
.El
.Sh SEE ALSO
.Xr accept 2 ,

7
sys/kern/sys_generic.c
View File

@ -1339,6 +1339,13 @@ kern_poll(struct thread *td, struct pollfd *ufds, u_int nfds,
} else
sbt = -1;
/*
* This is kinda bogus. We have fd limits, but that is not
* really related to the size of the pollfd array. Make sure
* we let the process use at least FD_SETSIZE entries and at
* least enough for the system-wide limits. We want to be reasonably
* safe, but not overly restrictive.
*/
if (nfds > maxfilesperproc && nfds > FD_SETSIZE)
return (EINVAL);
if (nfds > nitems(stackfds))