identical mmap programs in C and go
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June 10, 2024 17:31
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mmap examples
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <unistd.h> | |
#include <fcntl.h> | |
#include <sys/types.h> | |
#include <sys/stat.h> | |
#include <sys/mman.h> | |
int main () { | |
const char* filename = "main.c"; | |
int offset = 10; | |
int fd = open(filename, O_RDONLY); | |
if (fd == -1) { | |
printf("cannot open %s\n", filename); | |
return -1; | |
} | |
struct stat sbuf; | |
if (stat(filename, &sbuf) == -1) { | |
printf("cannot stat %s\n", filename); | |
return -1; | |
} | |
int size = sbuf.st_size; | |
char* data = mmap((caddr_t)0, size, PROT_READ, MAP_SHARED, fd, 0); | |
if (data == -1) { | |
printf("cannot mmap %s\n", filename); | |
return -1; | |
} | |
printf("byte at offset %d is %c\n", offset, data[offset - 1]); | |
int err = munmap(data, size); | |
if (err == -1) { | |
printf("cannot munmap %s\n", filename); | |
return -1; | |
} | |
return 0; | |
} |
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package main | |
import ( | |
"fmt" | |
"os" | |
"syscall" | |
) | |
func main() { | |
filename, offset := "main.c", 10 | |
f, err := os.Open(filename) | |
if err != nil { | |
panic(err) | |
} | |
fd := int(f.Fd()) | |
stat, err := f.Stat() | |
if err != nil { | |
panic(err) | |
} | |
size := int(stat.Size()) | |
b, err := syscall.Mmap(fd, 0, size, syscall.PROT_READ, syscall.MAP_SHARED) | |
if err != nil { | |
panic(err) | |
} | |
fmt.Printf("%c\n", b[offset-1]) | |
err = syscall.Munmap(b) | |
if err != nil { | |
panic(err) | |
} | |
} |
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package main | |
import ( | |
"os" | |
"syscall" | |
) | |
func main() { | |
filename, offset, length := "testgo.out", 10, 20 | |
f, err := os.Create(filename) | |
if err != nil { | |
panic(err) | |
} | |
f.Write(make([]byte, length)) | |
fd := int(f.Fd()) | |
b, err := syscall.Mmap(fd, 0, length, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED) | |
if err != nil { | |
panic(err) | |
} | |
b[offset-1] = 'x' | |
err = syscall.Munmap(b) | |
if err != nil { | |
panic(err) | |
} | |
} |
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