Hello I have a scenario where the only thing I should do is to output data and I must use DMA. Which one is the best option ifI only have to output data,write back or write through and why? Thank you!
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I am trying to do animation in the terminal by printing and flushing repeatedly. Is there a way to flush the standard output after writing to it in ATS?
Thank you!
I suppose that you can just do
val () = fileref_flush(stdout_ref)
If you need to do this all the time, then you may want to use 'setbuf' to disable buffering.
I want to copy an integer variable from user space to kernel space.
Can anyone give me a simple example how to do this?
I came to know that we can use get_user but i am unable to know how..
Check man pages of copy_to_user and copy_from_user.
Write a simple kernel module, with read/write operations, and register and char device for them, something like /dev/sample.
Do an application write/read, on fd opened by this application.
Now you need to implement the mechanism for transferring this data to kernel space and read back whatever returned.
- In write you do a copy_from_user, before this check passed buffer is valid or not.
- In read you do a copy_to_user.
Make sure error conditions are taken care of, and open call implementation should keep track of how many opens are there, if you want to implement multiple open, and this count should be decremented, when application calls a close on opened FD.
Do you follow ?
I wrote some simple code to learn the structure of a TCPSocket. I thought it's like an IO stream so I tried to use seek to move the "reading position" back a byte:
socket.gets #=> hello world
socket.seek(-5, IO::SEEK_CUR)
socket.gets #=> hello world # this should return world
but, it gives me an error:
server.rb:11:in `seek': Illegal seek (Errno::ESPIPE)
Does anyone have an idea why this doesn't work?
If this was the case then the socket needs to keep all data around if someone would decides to seek backwards (and how would forward seek work, block for more data?). You could probably quite easy write a wrapper class around a socket that keeps track of a position and also buffers all data or blocks if needed etc.
But maybe you could try to use IO#bytes or IO#chars in combination with Enumerator#peek?
TCP/IP would be more like having a series of files on disk, where you can only read forward a file at a time. The files have to be read sequentially, and you can't jump ahead or back. It's not capable of random I/O, like you can do on a disk, it's more like a serial connection you can only read as things appear.
In order to do what you want you have to build a buffer, where you append each block (i.e., file), reconstructing the entire message. If you want to look backwards at any point, you have to look in your buffer. If you want to look forward you have to wait for that block to be received and read and appended.
That's a simple explanation. It's possible to request blocks be resent in IP but really, at the level we normally work at, we're only reading forward.
I'm streaming data in a pig script through an executable that returns an xml fragment for each line of input I stream to it. That xml fragment happens to span multiple lines and I have no control whatsoever over the output of the executable I stream to
In relation to Use Hadoop Pig to load data from text file w/ each record on multiple lines?, the answer was suggesting writing a custom record reader. The problem is, this works fine if you want to implement a LoadFunc that reads from a file, but to be able to use streaming, it has to implement StreamToPig. StreamToPig allows you to only read one line at a time as far as I understood
Does anyone know how to handle such a situation?
If you are absolutely sure, then one option is to manage it internally to the streaming solution. That is to say, you build up the tuple yourself, and when you hit whatever your desired size is, you do the processing and return a value. In general, evalfuncs in pig have this issue.
I have a Win32 application written in C that can have its console output via printf() redirected to a log file.
It would be nice if I could have my app. detect if it had been started with or without a redirect '>'.
Any ideas?
Tom, thanks for the input.
I did some experiments and found this works for me..
fpost_t pos ;
fgetpos (stdout, & pos) ;
When an application's output is being redirected to a file, fgetpos() sets 'pos' to zero. It makes sense since its freshly opened stderr for you. EDIT: Actually, the value returned may be a positive integer if text has already been redirected to the log/file. So in your code you'd have something like "if (pos >= 0) bfRedirected = TRUE ;"
When an application's output is not being redirected - it's going to the console device - not a file, so fgetpos() will set 'pos' to -1.
I think that pipes are blind by nature, so you don't have a built-in way to tell whether you're being redirected. Moreover, trying to find out what's happening behind an abstraction layer is a bad habit.
If you really need to control your output, add the log file name as a command line parameter!
That being said, you can make some smart guesswork to find out:
A program can query the shell command history to find out the most recent commands executed.
If you know the path to the logfiles, you can scan that directory and see if a file has been created or changed its size.
Benchmark writing speed when redirected and not redirected. This would work only if your system is ultra-stable, and environment condition won't change.
There may be a way to do this - a quick google yielded this hit that might give you the hint in the right direction.
Method from Microsoft: WriteConsole fails if it is used with a standard handle that is redirected to a file. If an application processes multilingual output that can be redirected, determine whether the output handle is a console handle (one method is to call the GetConsoleMode function and check whether it succeeds).
AFAIK the answer to this is that you can't. Output redirection works by simply reading the stream of output from a given program and redirecting it to another pipe / stream. The design of file / streams is such that the writer is ignorant of the reader to the point that you shouldn't know you are being read.
Even detecting that there was a reader would be of no use because there is one in the normal case. The console is reading the output of your program and displaying it to the screen already.