I would like to understand if there are any conventions set up in kernel programming when creating network interfaces in the kernel and initializing interface flags, such as IFF_UP, or IFF_MULTICAST etc. What flags must be configured at minimum -- is there any requirement for this?
Thanks.
Take a look at http://man7.org/linux/man-pages/man7/netdevice.7.html, which is the man page for NETDEVICE(7). In there, you will see a list of flags under SIOCSIFFLAGS and SIOCCIFFLAGS.
Standard interface flags are described at include/linux/if.h.
See comments for details.
Related
I am evaluating Keil Microvision IDE on STM32H753.
I am doing compiler comparison between ARMCC5 and AC6 in the different optimisation levels. AC6 is based on Clang.
My code is not using memcpy and I have unchecked "Use MicroLIB" in the project settings , However a basic byte per byte copy loop in my code is replaced by a memcpy with AC6 (only in "high" optimisation levels). It doesn't happen with ARMCC5.
I tried using compilation options to avoid that, as described here: -ffreestanding and -disable-simplify-libcalls, at both compiler and linker levels but it didn't change (for the second option, I get an error message saying that the option is not supported).
In the ARMCLANG reference guide i've found the options -nostdlib -nostdlibinc that prevent (??) the compiler to use any function of a standard lib.
However I still need the math.h function.
Do you know how to prevent clang to use functions from the Standard C Lib that are not explicitely called in the code ?
EDIT: here is a quick and dirty reproduceable example:
https://godbolt.org/z/AX8_WV
Please do not discuss the quality of this example, I know it is dumb !!, I know about memset, etc... It is just to understand the issue
gcc know a lot about the memcpy, memset and similar functions and even they are called "the builtin functions". If you do not want those functions to be used by default just use the command line option -fno-builtin
https://godbolt.org/z/a42m4j
While looking at the statistics for CouchBase monitoring, like ep_queue_size, vb_num_eject_replicas, ep_warmup_value_count, and vb_active_curr_items, I see that most of them are prefixed with ep_ or vb_. I have not been able to find any explanation on what these prefixes mean.
I have tried searching the docs at https://docs.couchbase.com/server/current/manage/monitor/monitoring-cli.html but have found nothing. I think it might be that ep_ stands for ephemeral bucket and vb_ stands for vBucket, but that's just a wild guess.
ep refers to Eventually Persistent, referring to the eventually persistent data layer of Couchbase. Reference to it is here.
vb refers to vBucket. Reference to it is here.
I have a little Java program. I build a binary using Graal's native-image (i.e. GraalVM AOT aka SubstrateVM).
My program can be executed either with a Java runtime or from the native-image binary. What's the best way to tell which context I'm running in?
(This might be a bad practice in general but I believe it's inevitable/necessary in certain not-uncommon circumstances.)
Edit: There is now an API for that. See user7983712's answer.
The way it's done in the GraalVM is by capturing the com.oracle.graalvm.isaot system property: it is set to true while building AOT images. If you combine that with the fact that static initializers run during image generation, you can use
static final boolean IS_AOT = Boolean.getBoolean("com.oracle.graalvm.isaot")
This boolean will remain true when running the native image.
This is also useful to cut-off paths that you don't want in the final output: for example if you have some code that uses a feature that SVM doesn't support (e.g., dynamic class-loading) you can predicate it with !IS_AOT.
GraalVM now provides an API for checking the AOT context:
ImageInfo.inImageCode()
ImageInfo.inImageRuntimeCode()
ImageInfo.inImageBuildtimeCode()
ImageInfo.isExecutable()
ImageInfo.isSharedLibrary()
I'm leaning towards checking the presence/absence of some system properties. When I print out the system properties under Graal AOT I see:
{os.arch=x86_64, file.encoding=UTF-8, user.home=/Users/thom, path.separator=:, os.name=Mac OS X, user.dir=/Users/thom, line.separator=
, sun.jnu.encoding=UTF-8, file.separator=/, java.io.tmpdir=/var/folders/0x/rms5rjn526x33rm394xwmr8c0000gn/T/, user.name=thom}
As you may notice it's fairly short and is missing all the usual java.* ones such as java.class.path. I'll omit listing the lengthy Java version and instead link to another SO listing the usual Java System properties:
What is the full list of standard keys recognized by the Java System.getProperty() method?
So one way to do it would seem to be to check whether one or more of the java.* properties are absent.
AFAIK there are no plans to set these in SubstrateVM. But System properties are mutable so one could possibly choose to fake them.
But anyway here's a way to do it:
def isGraalAOT = System.properties.getProperty("java.class.path") == null
I'm trying to run the readwrite example in the dsplink on the beagleboard. To do so, I need to give the dsp address as a command line parameter. How do I know what is the dsp address?
I have the config file of OMAP5030. Here's a snapshot of the dsplink memory section diagram (copied from CFG_OMAP3530_SHMEM.c):
If you must use readwrite, see this. You will want to look at .tcf files or such. However, as mentioned by TI engineers, readwrite is a very dangerous example to use. Look to MSGQ or other examples like that.
I am building a native Bonjour / Zeroconf library and need to build DNS query records to broadcast off to the other machines. I have tried looking thru the Erlang source code but as I am relatively new to Erlang it gets kind of dense down the bowels of all the inet_XXX.erl and .hrl files. I have a listener that works for receiving and parsing the DNS record payloads, I just can't figure out how to create the query records. What I really need to know is what I need to pass into inet_dns:encode() to get a binary I can send out. Here is what I am trying to do.
{ok,P} = inet_dns:encode(#dns_query{domain="_daap._tcp.local",type=ptr,class=in})
here is the error I am getting
10> test:send().
** exception error: {badrecord,dns_rec}
in function inet_dns:encode/1
in call from test:send/0
11>
I finally figured it out.
send(Domain) ->
{ok,S} = gen_udp:open(5555,[{reuseaddr,true}, {ip,{224,0,0,251}}, {multicast_ttl,4}, {multicast_loop,false}, {broadcast,true}, binary]),
P = #dns_rec{header=#dns_header{},qdlist=[#dns_query{domain=Domain,type=ptr,class=in}]},
gen_udp:send(S,{224,0,0,251},5353,inet_dns:encode(P)),
gen_udp:close(S).
The fact that there is no documentation for the inet_dns module should make you very wary of using it from your code. I hope you are fully aware that no consideration will be taken to your project if they (the OTP team) feel like changing how the module is implemented and used.
Read the code for implementation ideas, or just get down to creating the DNS protocol message using the Erlang bit syntax based on the RFCs on the DNS protocol. Creating a DNS package is much easier than parsing it (I've been down that road myself, and the "clever tricks" to minimize packet size hardly seem worth it).
As explained by Magnus in the Erlang Questions Mailing list:
http://groups.google.com/group/erlang-programming/browse_thread/thread/ce547dab981219df/47c3ca96b15092e0?show_docid=47c3ca96b15092e0
you were passing a dns_query instead of a dns_rec record in the encode/1 function.