I'm reminded of the old story... A man decides to learn how to juggle, so gets a book on it. Page one, it says "pick up one ball, throw it from the left hand to the right hand and back, and don't let it hit the ground". So he does and turns the page. It tells him to pick up two balls, and he does, and it works. The next pages tell him to pick up three, four, and finally, five -- but someone had torn out the rest of the pages, so he never learns how to juggle twelve.
To map two files, you call mmap twice, on two different file descriptors. To map five files, you call mmap five times, on five different file descriptors. And so forth.
And if you really have a lot of them, you could read filenames from a file and store the file descriptors and mmap-ed memory pointers in an array or vector.
You could also structure your data, so you can keep more than one thing in a single file instead of mapping lots of seperate ones.
Also keep in mind there are limits to the amount of memory you can map on a 32-bit system. Keep one process below a few hundred megs and you should be relatively safe. Now 64-bit systems, they can safely map truly absurd amounts of memory -- xfs.fsck can map in entire multi-terabyte disk arrays to do its dirty work, for example, but crashes if you try it on a 32-bit system.
Last edited by Corona688; 01-20-2011 at 11:38 AM..
I'm new to kernels and C, and I am tinkering around trying to understand OpenBSD's secure memory management. I'm stumped on a couple points.
I've read up on malloc() which was apparently modified years ago to allocate memory using mmap. First question, that would be this here, right?
... (4 Replies)
I want to know whether this is possile or ever been tried out.
I want to obtain a chuck of memory using mmap()
I do it so :
n = mmap(0, 8000, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
And hold on to that memory, when a process requests for memory, some memory is... (2 Replies)
Hi
I want to lock or prevent a portion of memory which I allocated. So I tried MLOCK, MPROTECT and some like this. But all these functions works only on page border. Can I know why that so.
Is that possible to protect a portion of memory which is in middle of the page.
Example.
int A;
... (1 Reply)
Descriptions:
Develop a program that uses mmap() to map a file to memory space. Prepare such a file by yourself and do the follows.
<LI class=MsoNormal>Display the content of the file after mapping; <LI class=MsoNormal>Output how many digits included in the file; <LI class=MsoNormal>Replace... (1 Reply)
Dear Experts,
i have a problem related to mmap(), when i run my program on sun for 64 bit which is throwing SIGBUS when it encounters mmap() function, what is the reason how to resolve this one, because it is working for 32 bit.
with regards,
vidya. (2 Replies)
I'm using select() to monitor multiple file descriptors (inet sockets) in application. But this application must also collaborate with other applications on the same host via shared memory (mmap'ed file) due to performance reasons. How can I become notification that mmaped memory is changed or... (1 Reply)
We recently have been seeing the following type of error on our development server. Being somewhat new to HP-UX I was hoping to get some insight. Here is what I have found.
I have been doing some research.
/usr/lib/dld.sl: Call to mmap() failed - TEXT /u07/mdev/lib/libCLEND.sl... (2 Replies)
Hello. I'm writing some random access i/o software on Solaris 8 using mmap64 to memory map large files (my test file is ~25 GB).
The abbreviated code fragment is:
fd = open(cbuf,O_RDONLY|O_LARGEFILE);
struct stat statbuf;
fstat(fd,&statbuf);
off_t len =... (0 Replies)