Hello Chris,
Am 28.03.21 um 04:43 schrieb Chris Johns:
On 22/3/21 7:45 pm, Christian MAUDERER wrote:
Hello Chris,
Am 19.03.21 um 02:11 schrieb Chris Johns:
On 3/3/21 7:41 pm, Christian MAUDERER wrote:
Hello Chris,
Am 03.03.21 um 02:17 schrieb Chris Johns:
On 2/3/21 7:26 pm, Christian MAUDERER wrote:
Hello Chris,
Am 02.03.21 um 01:03 schrieb Chris Johns:
On 1/3/21 7:24 pm, Christian MAUDERER wrote:
Hello Chris,
thanks for the review.
Am 26.02.21 um 19:04 schrieb Chris Johns:
On 26/2/21 2:01 am, Christian Mauderer wrote:
Dynamically allocate a big enough file descriptor set for select(). A
better solution would be to use kqueue() instead of select().
---
.../racoon/rtems-bsd-racoon-session-data.h | 6 +--
ipsec-tools/src/racoon/session.c | 40
+++++++++++++++++++
2 files changed, 43 insertions(+), 3 deletions(-)
diff --git a/ipsec-tools/src/racoon/rtems-bsd-racoon-session-data.h
b/ipsec-tools/src/racoon/rtems-bsd-racoon-session-data.h
index b869a1518..196107a35 100644
--- a/ipsec-tools/src/racoon/rtems-bsd-racoon-session-data.h
+++ b/ipsec-tools/src/racoon/rtems-bsd-racoon-session-data.h
@@ -2,11 +2,11 @@
#include <rtems/linkersets.h>
#include "rtems-bsd-racoon-data.h"
/* session.c */
-RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static fd_set active_mask);
-RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static fd_set preset_mask);
+RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static _types_fd_set
*allocated_active_mask);
+RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static _types_fd_set
*allocated_preset_mask);
RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static int nfds);
RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static int signals[]);
RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static sig_atomic_t
volatile
volatile sigreq[]);
-RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static struct fd_monitor
fd_monitors[]);
+RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static struct fd_monitor
*allocated_fd_monitors);
RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static struct
fd_monitor_list
fd_monitor_tree[]);
RTEMS_LINKER_RWSET_CONTENT(bsd_prog_racoon, static struct sched
scflushsa);
diff --git a/ipsec-tools/src/racoon/session.c
b/ipsec-tools/src/racoon/session.c
index 65124c15e..90120c761 100644
--- a/ipsec-tools/src/racoon/session.c
+++ b/ipsec-tools/src/racoon/session.c
@@ -65,6 +65,10 @@
#include <sys/stat.h>
#include <paths.h>
#include <err.h>
+#ifdef __rtems__
+#include <sys/param.h>
+#include <rtems/libio_.h>
+#endif /* __rtems__ */
#include <netinet/in.h>
#include <resolv.h>
@@ -123,8 +127,16 @@ static void check_sigreq __P((void));
static void check_flushsa __P((void));
static int close_sockets __P((void));
+#ifndef __rtems__
static fd_set preset_mask, active_mask;
static struct fd_monitor fd_monitors[FD_SETSIZE];
+#else /* __rtems__ */
+static fd_set *allocated_preset_mask, *allocated_active_mask;
+static struct fd_monitor *allocated_fd_monitors;
+#define preset_mask (*allocated_preset_mask)
+#define active_mask (*allocated_active_mask)
+#define fd_monitors (allocated_fd_monitors)
+#endif /* __rtems__ */
static TAILQ_HEAD(fd_monitor_list, fd_monitor)
fd_monitor_tree[NUM_PRIORITIES];
static int nfds = 0;
@@ -134,7 +146,11 @@ static struct sched scflushsa =
SCHED_INITIALIZER();
void
monitor_fd(int fd, int (*callback)(void *, int), void *ctx, int
priority)
{
+#ifndef __rtems__
if (fd < 0 || fd >= FD_SETSIZE) {
+#else /* __rtems__ */
+ if (fd < 0 || fd >= rtems_libio_number_iops) {
+#endif /* __rtems__ */
plog(LLV_ERROR, LOCATION, NULL, "fd_set overrun");
exit(1);
}
@@ -158,7 +174,11 @@ monitor_fd(int fd, int (*callback)(void *, int), void
*ctx, int priority)
void
unmonitor_fd(int fd)
{
+#ifndef __rtems__
if (fd < 0 || fd >= FD_SETSIZE) {
+#else /* __rtems__ */
+ if (fd < 0 || fd >= rtems_libio_number_iops) {
+#endif /* __rtems__ */
plog(LLV_ERROR, LOCATION, NULL, "fd_set overrun");
exit(1);
}
@@ -186,7 +206,22 @@ session(void)
struct fd_monitor *fdm;
nfds = 0;
+#ifndef __rtems__
FD_ZERO(&preset_mask);
+#else /* __rtems__ */
+ allocated_preset_mask = calloc(sizeof(fd_set),
+ howmany(rtems_libio_number_iops, sizeof(fd_set) * 8));
Does `maxfiles` work here?
To be honest: I'm not sure.
According to the comment in file.h:
extern int maxfiles; /* kernel limit on number of open files */
Yes.
Sounds like it _can_ be the same as the maximum file number but doesn't
have to.
I think we need to have them be the same value.
I didn't find where we implement it. It's declared as an extern int
maxfiles but
I didn't find any definition. I found it only in libbsd in
freebsd/sys/kern/uipc_socket.c where it is defined like follows:
#define maxfiles rtems_libio_number_iops
Ah OK. I knew it had been assigned somewhere and yes it looks like it is
local
to that file.
So question is: Where and how is maxfiles defined?
I have provided a value in the rtemsbsd init file as part of the set og
globals
we need to maintained.
Somehow I missed that. Where can I find it?
Again sorry, I was in a rush and I was not clear. I have add this in my new
changes for NFSv4 support and this is what I sorted out.
Ah, OK. In that case I'll keep the rtems_libio_number_iops at the moment if it
is OK for you.
Yes that is fine.
Thanks.
+ if (allocated_preset_mask == NULL)
+ errx(1, "failed to allocate preset_mask");
+ allocated_active_mask = calloc(sizeof(fd_set),
+ howmany(rtems_libio_number_iops, sizeof(fd_set) * 8));
+ if (allocated_active_mask == NULL)
+ errx(1, "failed to allocate active_mask");
+ allocated_fd_monitors = calloc(
+ rtems_libio_number_iops, sizeof(struct fd_monitor));
+ if (allocated_fd_monitors == NULL)
+ errx(1, "failed to allocate fd_monitors");
At the core of this issue is the rotating fd allocation that we have in
libio. A
report from a FreeBSD machine I have is:
$ sysctl -a | grep maxfiles
kern.maxfiles: 1037243
kern.maxfilesperproc: 933516
I doubt a select process in FreeBSD needs a select array with that many
bits. I
have added similar code else where but I am wondering if this is really
what we
want to do. A side effect for us is the stack usage is not bounded and that
is a
problem. I think our newlib based max setting is too small.
I think we have to distinguish between FreeBSD kernel space and user space.
If I
have seen it correctly, FreeBSD uses kqueues or maybe sometimes poll
instead of
select in kernel space most of the time. That avoids the problem with big
file
numbers.
Yes kqueue is nice but we need to support existing code and this is a primary
role libbsd needs to perform. The lack is signals in libbsd is another
source of
issue.
I didn't want to say that we should not support select. I only wanted to say
that FreeBSD most likely just avoids that problem in kernel space so that they
don't have to support a select with 1037243 files. In user space they limit a
select to 1024 files.
Yes they do. My suggestion of us using 1024 is FreeBSD applications are fine
with this then they should be portable to RTEMS and libbsd and the need for us
to patch code is removed.
1024 for a select is quite much for an embedded system. It means that we will
need 128 bytes of stack for each select call in the future. It's a quite big
change.
The select call in LibBSD double this internally.
Doesn't make it better.
No it does not and I feel these hacks are just that hacks and average ones that
need to be removed.
Another possibility would be 256 (32 bytes) like some other *BSD do.
Maybe we should start a new discussion thread about the right FD_SETSIZE so that
more developers get involved?
Default for FreeBSD seems to be a FD_SETSIZE of 1024. See the Notes
section in
the select man page:
https://www.freebsd.org/cgi/man.cgi?query=select&sektion=2&manpath=freebsd-release-ports#end
Yes.
I think select is used in user space applications most of the time. I would
guess that FreeBSD has some file number mapping between kernel and user
space
that would allow every application to open 1024 files.
Yes. There are other checks and arrays in the kernel's select that handle the
size of 1024 or smaller. We should align ourselves with FreeBSD. A select
call
uses a lot of stack.
I have no problem if we align more with FreeBSD. But I'm not sure how much
effort that would be. And we have to be careful not to increase the memory
usage
for small targets too much.
We need to find a path between that sort of space optimization and the
functionality libbsd brings. The select call is costly in terms of stack
size as
the kern_select call has:
/*
* The magic 2048 here is chosen to be just enough for FD_SETSIZE
* infds with the new FD_SETSIZE of 1024, and more than enough for
* FD_SETSIZE infds, outfds and exceptfds with the old FD_SETSIZE
* of 256.
*/
fd_mask s_selbits[howmany(2048, NFDBITS)];
I do not know if this means we need to be more concerned about the size of
less.
Hm. They could have used FD_SETSIZE instead of the magic value with a comment...
It might pay to check the surrounding code a litte more before raising something
like that on the FreeBSds hackers list. There are subtle optimisations happening
to make this call perform.
I didn't plan to rise it on the FreeBSD mailing list. If I plan to fight against
existing magic numbers I'll start in RTEMS before I fight them in FreeBSD ;-)
Yes. My point is we are porting as clean FreeBSD code as we can have and this is
what we inherit.
I think a big problem for RTEMS is that we have shared file numbers for all
processes. This makes 1024 a lot less compared to starting from 0 for every
process.
We are a single process so I do not follow. We are no different to other
processes. We have lived with a small file set size for years until libio was
changed to cycle over the fd numbers
We started to include libbsd with some applications that are more used to
desktop or server environments like wpa supplicant or racoon. These applications
originally didn't expect to run in a single process environment but have an own
process for each of them.
I'm just not sure whether increasing FD_SETSIZE is the best solution for that
problem. It only moves it so that it does happen in fewer applications at the
cost that all applications that use select and can work with the current limit
will need more stack.
You could be right maybe the issue is not specially there but in libio.
That means: I wouldn't object to such a patch but I don't want to be the one
creating and suggesting it.
Sure, this is your choice to make. I have raised this issue with Sebastian and
now you and both have supported this approach to fixing select.
Because, although the kind of fix is more a hack, it can solve the
problem for these use cases. They allow libbsd to be used regardless of
the fd_set size. Of course it has the downside that it increases the
maintenance effort for libbsd (like every patch does) and therefore it
is not an ideal solution.
I have given this topic some more consideration and the FD size is just a rubber
band. The reality is the FD set needs to always be the libio size because of the
way our select and file system are implement and this not how select has been
defined.
Agreed: The big problem is that the FD set _should_ be the same as libio
size. But at the same time it's used for a fixed type. If that type is
used in a structure in a library, we can't base it on one of our
CONFIGURE_* macros.
Theoretically we could try to somehow define it as a pointer (or head of
a list or simmilar) and allocate space as soon as someone adds something
to the list. But I'm not sure where we could free that kind of memory.
And I'm also sure that there are quite some edge cases that wouldn't
work with that.
As things stand select is broken and this is a bug. We cannot redefine
select so we need to live with how it works. I think backing out libio
incrementing fd to catch fd reuse is seriously on the table. The side effects
out way the benefits.
How much time do you think would be necessary for this kind of change?
This sounds like a complex but very self-contained toppic. Do you think
we could convince a (good) GSoC student to do that? Of course it would
need a thourough review at such a critical location and therefore would
be quite a bit of work for the mentor too.
This exmple explains the bug. Set the FD set size to 1024 to match FreeBSD, it
cannnot be any larger. Set the libio descriptors to 2048. Open and close a file
1025 times. Open a single socket and call select. Select will fail and we have
only 1 extra fd on top of stdio ones.
There are of course other issues with select such as no more than 64, or 1024 if
changing the default, fd's being open but that is historical. If it is arugued
this is an issue that should be resolved then it should also include the fixed
size in the FreeBSD kernel and that being raised and resolved there. After that
we have the lack of signal support in libbsd.
I feel the change you have pushed is the result of looking under the hood and
inspecting the implenmentation to avoid a select bug.
Yes, it is. It is very specific to the implementation of select.
FYI I have a major set of changes to libbsd that enables FreeBSD descriptor
support and moves the libio support to specific interfaces.
OK. When do you plan to add that and to which branches?
I am looking 6-freebsd-12 and master. Thses changes are a major rework and
not
suitable for 5.
I assumed that.
I would like to add this
patch set to 5 sooner or later because it fixes a potential bug in racoon
for
that branch too.
Sorry I missed this for 5. I will need to think about this on 5. I do not
think
it is a problem but I am not sure about it on 6 and beyond. I would prefer we
consider a better fix for select that the limited 64 descriptors we currently
have.
Maybe we should take a multi step approach:
Use the workaround like I suggested for 5 and (at the moment) for master. A
similar workaround is already used in quite some other locations in libbsd. So
it's not a new method.
Start a ticket and a discussion for a better solution.
Sounds a good approach. I am fine with the changes because it is what we
have to
do and this was not meant to halt the progress, rather I wanted to have the
discussion and raise the concerns.
OK. Thanks.
If you don't add further objections, I'll create a ticket for the patch and
apply it in the next days. I'll create an extra ticket and mail thread for
applying it to 5 afterwards.
Sorry I have been busy with GSoC and other things and could not get back to
this. I see you have pushed this change so it is done.
I am going NACK all similar select changes in future. At least you have some
certianty. This includes updates to ping and ping6 on 6. The patch on the 5
branch is OK because it fixes a bug however for 6 and libbsd master we need to
look foward and resolve this issue. Basically for me this type of change is a
dead end.
Currently most selects in libbsd are fixed with the workarround. But we
still have a select in wpa_supplicant and I'm sure that we get the
problem in the future too. So if you want to continue a discussion for a
clean solution, we could do that for wpa_supplicant. Note that I
currently don't have a fundet project for wpa_supplicant so that would
be hobby time.
Best regards
Christian
Chris
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