Category Archives: Source

Alexander Leidinger

A while ago I committed the linuxulator D-Trace probes I talked about earlier. I waited a little bit for this announcement to make sure I have not broken anything. Nobody complained so far, so I assume nothing obviously bad crept in.

The >500 probes I committed do not cover the entire linuxulator, but are a good start. Adding new ones is straight forward, if someone is interested in a junior–kernel–hacker task, this would be one. Just ask me (or ask on emulation@), and I can guide you through it.


Alexander Leidinger

In case you have not noticed yet, KDTRACE_HOOKS is now in the GENERIC kernel in FreeBSD-current. This means you just need to load the DTrace modules and can use DTrace with the GENERIC kernel.

In case you do not know what you can do with DTrace, take the time to have a look at the DTrace blog. It is worth any minute you invest reading it.


Alexander Leidinger

This weekend I made some progress in the linuxulator:

  • I MFCed the reporting of some linux-syscalls to 9-stable and 8-stable.
  • I updated my linuxulator-dtrace patch to a recent -current. I already compiled it on i386 and arundel@ has it compiled on amd64. I counted more than 500 new DTrace probes. Now that DTrace rescans for SDT probes when a kernel module is loaded, there is no kernel panic anymore when the linux module is loaded after the DTrace modules and you want to use DTrace. I try to commit this at a morning of a day where I can fix things during the day in case some problems show up which I did not notice during my testing.
  • I created a PR for portmgr@ to repocopy a new linux_base port.
  • I set the expiration date of linux_base-fc4 (only used by 7.x and upstream way past its EoL) and all dependent ports. It is set to the EoL of the last 7.x release, which can not use a later linux_base port. I also added a comment which explains that the date is the EoL of the last 7.x release.


New opportunities in the linuxulator

Last weekend I committed some dummy-syscalls to the linuxulator in FreeBSD-current. I also added some comments to syscalls.master which should give a hint which linux kernel had them for the first time (if the linux man–page I looked this up in is correct). So if someone wants to experiment with a higher compat.linux.osrelease than 2.6.16 (as it is needed for a CentOS based linux_base), he should now get some kernel messages about unimplemented syscalls instead of a silent failure.

There may be some low-hanging fruits in there, but I did not really verify this by checking what the dummy syscalls are supposed to do in linux and if we can easily map this to existing FreeBSD features. In case someone has a look, please send an email to


Static DTrace probes for the linuxulator updated

I got a little bit of time to update my 3 year old work of adding static DTrace probes to the linuxulator.

The changes are not in HEAD, but in my linuxulator-dtrace branch. The revision to have a look at is r230910. Included are some DTrace scripts:

  • script to check internal locks
  • script to trace futexes
  • script to generate stats for DTracified linuxulator parts
  • script to check for errors:
    • emulation errors (unsupported stuff, unknown stuff, …)
    • kernel errors (resource shortage, …)
    • programming errors (errors which can happen if someone made a mistake, but should not happen)

The programming-error checks give hints about userland programming errors respectively a hint about the reason of error return values due to resource shortage or maybe a wrong combination of parameters. An example error message for this case is “Application %s issued a sysctl which failed the length restrictions.nThe length passed is %d, the min length supported is 1 and the max length supported is %d.n

(Free)BSD inside Android

Today I was looking into the OpenSource licenses which are displayed for Android (2.3.4). There are several files which come with a BSD license.

During looking at it, I noticed that the libm has the copyright of several FreeBSD people. I did not had an in-deep look if this is because they took the FreeBSD libm, or if this is because parts of the FreeBSD libm where adopted by other BSD projects.

What I noticed is, that some special characters are not displayed correctly. For example the name Dag-Erling Smørgrav looks mangled in the display of the license inside the phone (I hope it is displayed better in my blog). His name is not the only problem case, there are also other characters which are not rendered as expected.

This does not really look professional.


Linuxulator explained (for developers): adding ioctls directly to the kernel

After giving an overview of the in-kernel basics of the Linuxulator, I want now to describe how to add support for new ioctls to the Linuxulator.

Where are the files to modify?

The platform independent code for the ioctls is in SRC/sys/compat/linux/linux_ioctl.c. The defines to have names for the ioctl values are in SRC/sys/compat/linux/linux_ioctl.h.

How to modify them?

First of all create a new header which will contain all the structures, named values and macros for those new ioctls. As written above, the ioctl values (e.g. #define LINUX_VIDIOC_ENCODER_CMD 0x564d /* 0xc028564d */) do not belong there, they shall be added to linux_ioctl.h. During the course of adding support for ioctls, you will need this new header. Add it in the SRC/sys/compat/linux/ directory, and prefix the name with a linux_. It would be good to decide on a common tag here (referenced as yourtag in the following), and stay with it. Use it wherever you need to have some specific name for the ioctl-set you want to add. In this case it would result in linux_yourtag.h (or even linux_ioctl_yourtag.h, depending if this is used for something very specific to the ioctls, or some generic linux feature) as the name of the header file. This was not done in the past, so do not expect that the names inside the linux_ioctl.c file will be consistent to this naming scheme, but it is never too late to correct mistakes of the past (at least in Open Source software development).

Now add this header to linux_ioctl.c (you need to include compat/linux/linux_yourtag.h). After that add the ioctl values to linux_ioctl.h. As can be seen above, the defines should be named the same as on linux, but with a LINUX_ prefix (make sure they where not defined before somewhere else). The ioctl values need to be the same hex values as in Linux, off course. Sort them according to their hex value. When you added all, you need to add two more defines. The LINUX_IOCTL_yourtag_MIN and LINUX_IOCTL_yourtag_MAX ones. The MIN-one needs to be an alias for the first (sorted according to the hex value) ioctl you added, and MAX needs to be an alias for the last (again, sorted according to the hex value) ioctl you added.

The next step is to let the Linuxulator know that it is able to handle the ioctls in the LINUX_IOCTL_yourtag_MIN to LINUX_IOCTL_yourtag_MAX range. Search the static linux_ioctl_function_t section of linux_ioctl.c and add such a variable for your ioctl set. The name of the variable should be something like linux_ioctl_yourtag.

Similar for the handler-definition for this. Search the static struct linux_ioctl_handler section and add a yourtag_handler. Set it to { linux_ioctl_yourtag, LINUX_IOCTL_yourtag_MIN, LINUX_IOCTL_yourtag_MAX }. To make this handler known to the Linuxulator, you need to add it to the DATA_SET section. Add DATA_SET(linux_ioctl_handler_set, yourtag_handler) there.

Now the meat, the function which handles the ioctls. You already defined it as linux_ioctl_function_t, but now you need to write it. The outline of it looks like this:

static int
linux_ioctl_yourtag(struct thread *td, struct linux_ioctl_args *args)
        struct file *fp;
        int error;
        switch (args->cmd & 0xffff) {
        case LINUX_an_easy_ioctl:
        case LINUX_a_not_so_easy_ioctl:
                /* your handling of the ioctl */
                fdrop(fp, td);
                return (error);
        /* some more handling of your ioctls */
       return (ENOIOCTL);
        error = ioctl(td, (struct ioctl_args *)args);
        return (error);

An easy ioctl in the switch above is an ioctl where you do not have to do something but can pass the ioctl through to FreeBSD itself. The not so easy ioctl case is an ioctl where you need to do e.g. a fget(td, args->fd, &fp). This is just an example, there are also other possibilities where you need to do additional stuff before the return, or where you do not pass the ioctl to FreeBSD. A typical example of what needs to be done here is to copy values from linux structures to FreeBSD structures (and the other way too), or to translate between 64bit and 32bit. Linux programs on amd64 are 32bit executables and 32bit structures/pointers. To make this work on amd64, you need to find a way to map between the two. There are examples in the kernel where this is already the case. The more prominent examples in the 64bit<->32bit regard are the v4l and v4l2 ioctls.

The tedious part is to research if a translation has to be done and if yes what needs to be translated how. When this is done, most of the work is not so hard. The linux_yourtag.h should contain the structures you need for this translation work.

It is also possible to add ioctls in a kernel module, but this is not subject to this description (I will update this posting with a link to it when I get time to write about it).


(Free)BSD inside Android

Today I was looking into the OpenSource licenses which are displayed for Android (2.3.4). There are several files which come with a BSD license.

During looking at it, I noticed that the libm has the copyright of several FreeBSD people. I did not had an in-deep look if this is because they took the FreeBSD libm, or if this is because parts of the FreeBSD libm where adopted by other BSD projects.

What I noticed is, that some special characters are not displayed correctly. For example the name Dag-Erling Smørgrav looks mangled in the display of the license inside the phone (I hope it is displayed better in my blog). His name is not the only problem case, there are also other characters which are not rendered as expected.

This does not really look professional.


v4l2 support in the linuxulator now in 8-stable

I MFCed the v4l2 support in the linuxulator to 8–stable. This allows now to use v4l2–webcams in skype/flash on 8-stable too.


Video4Linux2 sup­port in FreeBSD (linuxulator)

I com­mit­ted the v4l2 sup­port into the lin­ux­u­la­tor (in 9-current). Part of this was the import of the v4l2 header from linux. We have the per­mis­sion to use it (like the v4l one), it is not licensed via GPL. This means we can use it in FreeBSD native dri­vers, and they are even allowed to be com­piled into GENERIC (but I doubt we have a dri­ver which could pro­vide the v4l2 inter­face in GENERIC).

The code I com­mit­ted is “just

DTrace probes for the Linuxulator updated

If someone had a look at the earlier post about DTrace probes for the Linuxulator: I updated the patch at the same place. The difference between the previous one is that some D-scripts are fixed now to do what I meant, specially the ones which provide statistics output.


New DTrace probes for the linuxulator

I forward ported my DTrace probes for the FreeBSD linuxulator from a 2008-current to a recent –current. I have not the complete FreeBSD linuxulator covered, but a big part is already done. I can check the major locks in the linuxulator, trace futexes, and I have a D-script which yells at a lot of errors which could happen but should not.

Some of my D-scripts need some changes, as real-world testing showed that they are not really working as expected. They can get overwhelmed by the amount of speculation and dynamic variables (error message: dynamic variable drops with non-empty dirty list). For the dynamic variables problem I found a discussion on the net with some suggestions. For the speculation part I expect similar tuning-possibilities.

Unfortunately the D-script which checks the internal locks fails to compile. Seems there is a little misunderstanding on my side how the D-language is supposed to work.

I try to get some time later to have a look at those problems.

During my development I stumbled over some generic DTrace problems with the SDT provider I use for my probes:

  • If you load the Linux module after the SDT module, your system will panic as soon as you want to access some probes, e.g. “dtrace –l

HOWTO: creating your own updated linux RPM for the FreeBSD linuxulator

Background info

The FreeBSD linux compatibility environment currently uses RPMs from Fedora 10. Unfortunately Fedora 10 is end of life since a while. For one of the RPMs (the pango one) we where aware of a security vulnerability. As we do not know if it is feasible to update the linuxulator ports to something more recent, I decided to setup a VM with Fedora 10 and generate a new RPM for the linux-f10-pango port. Thanks to Luchesar V. ILIEV for explaining me how to do this.

Setup of the VM

I used VirtualBox 4.0.4 on a Solaris 10 x86 machine. I configured a fixed size disk of 16 GB and kept the default network setup (after installing the guest tools / kernel modules I switched to virtio, as I was not able to do anything useful besides a ping) and RAM size. The CD/DVD drive was configured to use the image of the full Fedora 10 DVD for i386 systems.

Setup of Fedora 10

Booting the VM from the DVD leads to the graphical Fedora 10 install software (after chosing to install a new system on the console). There I accepted all the defaults, except for the software to install. I deselected the Office and Productivity group and selected the Software Development group. When I was asked if I want to install some additional RPMs I had a look at the complete list and installed some I thought are necessary. I do not remember anymore which ones I chose, but everything which looks related to RPM building is a good candidate.

After a while the install will be finished and you can boot into the new system (eject the DVD from the drive before reboot). After reboot chose to install the Guest Additions in the menu of the VM. This should mount the ISO image in the VM. As root execute the file for Linux. This will build some kernel modules for better integration (e.g. seamless integration of the mouse between your desktop and the VM). At this point I rebooted and configured virtio as the NIC. I also had to configure the network settings by hand, as the GUI tool did not safe all the settings correctly.

Update and install of required RPMs

After the VM was up and the network configured, I updated the entire system (chose System Update in the menu). To update the pango port, I had to install the libthai-devel RPM. I had the RPM for it (and all the files I need to build a new pango RPM) already downloaded, so I did a “yum install /path/to/rpm

Additional FEATURE macros on the way

It seems I have a bit of free time now to take care about some FreeBSD related things.

As part of this I already committed the UFS/FFS related FEATURE macros which where developed by kibab@ during the Google Summer of Code 2010. The network/ALTQ related FEATURE macros are in the hands of bz@, he already reviewed them and wants to commit them (with some changes) as part of his improvements of parts of the network related code.

The GEOM related FEATURE macros I just send some minutes ago to geom@ for review. All the rest went out to hackers@ for review. The rest in this case is related to AUDIT, CAM, IPC, KTR, MAC, NFS, NTP, PMC, SYSV and a few other things.

If everything is committed, it should look a bit like this if queried from userland (not all features are shown, those are just the ones which are enabled in the kernel in one of my machines):

kern.features.scbus: 1
kern.features.geom_vol: 1
kern.features.geom_part_bsd: 1
kern.features.geom_part_ebr_compat: 1
kern.features.geom_part_ebr: 1
kern.features.geom_part_mbr: 1
kern.features.kposix_priority_scheduling: 1
kern.features.kdtrace_hooks: 1
kern.features.ktrace: 1
kern.features.invariant_support: 1
kern.features.compat_freebsd7: 1
kern.features.compat_freebsd6: 1
kern.features.pps_sync: 1
kern.features.stack: 1
kern.features.sysv_msg: 1
kern.features.sysv_sem: 1
kern.features.sysv_shm: 1
kern.features.posix_shm: 1
kern.features.ffs_snapshot: 1
kern.features.softupdates: 1
kern.features.ufs_acl: 1


The FreeBSD-linuxulator explained (for developers): basics

The last post about the Linuxulator where I explained the Linuxulator from an user point of view got some good amount of attention. Triggered by a recent explanation of the Linuxulator errno stuff to a fellow FreeBSD developer I decided so see if more developers are interested in some more info too…

The syscall vector

In sys/linux/linux_sysvec.c is all the basic setup to handle Linux “system stuff

ZFS and NFS / on-disk-cache

In the FreeBSD mailinglists I stumbled over  a post which refers to a blog-post which describes why ZFS seems to be slow (on Solaris).

In short: ZFS guarantees that the NFS client does not experience silent corruption of data (NFS server crash and loss of data which is supposed to be already on disk for the client). A recommendation is to enable the disk-cache for disks which are completely used by ZFS, as ZFS (unlike UFS) is aware of disk-caches. This increases the performance to what UFS is delivering in the NFS case.

There is no in-deep description of what it means that ZFS is aware of disk-caches, but I think this is a reference to the fact that ZFS is sending a flush command to the disk at the right moments. Letting aside the fact that there are disks out there which lie to you about this (they tell the flush command finished when it is not), this would mean that this is supported in FreeBSD too.

So everyone who is currently disabling the ZIL to get better NFS performance (and accept silent data corruption on the client side): move your zpool to dedicated (no other real FS than ZFS, swap and dump devices are OK) disks (honest ones) and enable the disk-caches instead of disabling the ZIL.

I also recommend that people which have ZFS already on dedicated (and honest) disks have a look if the disk-caches are enabled.


v4l support in the linuxulator MFCed to 8-stable

I merged the v4l translation layer into the linuxulator of 8-stable. As in –current, this just means that linux apps (like Skype) can now use FreeBSD native devices which conform to the v4l ABI. The port multimedia/webcamd provides access to some webcams (or DVB hardware) via the v4l ABI.

People which want to test the linuxulator part should first make sure a native FreeBSD application has no problem accessing the device.


WITH_CTF is really usable now

I just committed a patch which makes WITH_CTF usable now.

Yes, you could use it before, but you had to remember to specify it at each build. Now you can add it to your kernel config (via makeoptions), and then you can forget about it.

Thanks to jhb and imp for review and suggestions.