ccan

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Module:

antithread/alloc

Summary:

memory allocator routines

Author:

Rusty Russell <rusty@rustcorp.com.au>

Dependencies:

Description:

The alloc module implements a simple allocator which you can use to dynamically allocate space within a region of memory. This can be useful for suballocations within a given region, or a memory-mapped file.

All metadata is kept within the memory handed to the allocator: you only need hand the pointer and the size of the memory to each call.

The region contents is always in offsets, so it can be mapped in different places, but is not endian-safe.

Example:

#include <sys/mman.h>
#include <unistd.h>
#include <sys/types.h>
#include <err.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <ccan/antithread/alloc/alloc.h>

static void usage(const char *name)
{
        errx(1, "Usage: %s --create <mapfile>\n"
             " %s --check <mapfile>\n"
             " %s --alloc <mapfile>\n"
             " %s --free=<offset> <mapfile>\n", name, name, name, name);
}

// Create a memory mapped file, and allocate from within it
int main(int argc, char *argv[])
{
        void *a, *p;
        int fd;
        enum { CREATE, CHECK, ALLOC, FREE } cmd;

        if (argc != 3)
                usage(argv[0]);

        if (strcmp(argv[1], "--create") == 0)
                cmd = CREATE;
        else if (strcmp(argv[1], "--check") == 0)
                cmd = CHECK;
        else if (strcmp(argv[1], "--alloc") == 0)
                cmd = ALLOC;
        else if (strncmp(argv[1], "--free=", strlen("--free=")) == 0)
                cmd = FREE;
        else
                usage(argv[0]);

        if (cmd == CREATE) {
                fd = open(argv[2], O_RDWR|O_CREAT|O_EXCL, 0600);
                if (fd < 0)
                        err(1, "Could not create %s", argv[2]);
                if (ftruncate(fd, 1048576) != 0)
                        err(1, "Could not set length on %s", argv[2]);
        } else {
                fd = open(argv[2], O_RDWR);
                if (fd < 0)
                        err(1, "Could not open %s", argv[2]);
        }

        a = mmap(NULL, 1048576, PROT_READ|PROT_WRITE, MAP_SHARED, fd,0);
        if (a == MAP_FAILED)
                err(1, "Could not map %s", argv[2]);

        switch (cmd) {
        case CREATE:
                alloc_init(a, 1048576);
                break;
        case CHECK:
                if (!alloc_check(a, 1048576))
                        err(1, "Region is corrupt");
                break;
        case ALLOC:
                p = alloc_get(a, 1048576, 1024, 16);
                if (!p)
                        errx(1, "Could not allocate");
                printf("%zu\n", (char *)p - (char *)a);
                break;
        case FREE:
                p = (char *)a + atol(argv[1] + strlen("--free="));
                alloc_free(a, 1048576, p);
                break;
        }
        return 0;
}

License:

LGPL (v2.1 or any later version)