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?
For the life of me, I can't track down source code for mmap(). I know that this is a kernel system call, but where is that source? In particular, I'm interested to see how mmap() now returns a randomized location in memory.
Last edited by Scott; 09-30-2013 at 05:26 PM..
Reason: Code tags
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)
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)
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)
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)
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)
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)
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)
Discussion started by: xerox
2 Replies
LEARN ABOUT FREEBSD
hashinit
HASHINIT(9) BSD Kernel Developer's Manual HASHINIT(9)NAME
hashinit, hashinit_flags, hashdestroy, phashinit -- manage kernel hash tables
SYNOPSIS
#include <sys/malloc.h>
#include <sys/systm.h>
#include <sys/queue.h>
void *
hashinit(int nelements, struct malloc_type *type, u_long *hashmask);
void
hashinit_flags(int nelements, struct malloc_type *type, u_long *hashmask, int flags);
void
hashdestroy(void *hashtbl, struct malloc_type *type, u_long hashmask);
void *
phashinit(int nelements, struct malloc_type *type, u_long *nentries);
DESCRIPTION
The hashinit(), hashinit_flags() and phashinit() functions allocate space for hash tables of size given by the argument nelements.
The hashinit() function allocates hash tables that are sized to largest power of two less than or equal to argument nelements. The
phashinit() function allocates hash tables that are sized to the largest prime number less than or equal to argument nelements. The
hashinit_flags() function operates like hashinit() but also accepts an additional argument flags which control various options during alloca-
tion. Allocated hash tables are contiguous arrays of LIST_HEAD(3) entries, allocated using malloc(9), and initialized using LIST_INIT(3).
The malloc arena to be used for allocation is pointed to by argument type.
The hashdestroy() function frees the space occupied by the hash table pointed to by argument hashtbl. Argument type determines the malloc
arena to use when freeing space. The argument hashmask should be the bit mask returned by the call to hashinit() that allocated the hash ta-
ble. The argument flags must be used with one of the following values.
HASH_NOWAIT Any malloc performed by the hashinit_flags() function will not be allowed to wait, and therefore may fail.
HASH_WAITOK Any malloc performed by the hashinit_flags() function is allowed to wait for memory.
IMPLEMENTATION NOTES
The largest prime hash value chosen by phashinit() is 32749.
RETURN VALUES
The hashinit() function returns a pointer to an allocated hash table and sets the location pointed to by hashmask to the bit mask to be used
for computing the correct slot in the hash table.
The phashinit() function returns a pointer to an allocated hash table and sets the location pointed to by nentries to the number of rows in
the hash table.
EXAMPLES
A typical example is shown below:
...
static LIST_HEAD(foo, foo) *footable;
static u_long foomask;
...
footable = hashinit(32, M_FOO, &foomask);
Here we allocate a hash table with 32 entries from the malloc arena pointed to by M_FOO. The mask for the allocated hash table is returned
in foomask. A subsequent call to hashdestroy() uses the value in foomask:
...
hashdestroy(footable, M_FOO, foomask);
DIAGNOSTICS
The hashinit() and phashinit() functions will panic if argument nelements is less than or equal to zero.
The hashdestroy() function will panic if the hash table pointed to by hashtbl is not empty.
SEE ALSO LIST_HEAD(3), malloc(9)BUGS
There is no phashdestroy() function, and using hashdestroy() to free a hash table allocated by phashinit() usually has grave consequences.
BSD October 10, 2004 BSD