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August 28, 2021 02:41
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Today I Learned: openat() https://yoursunny.com/t/2021/openat/
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#include <stdbool.h> | |
#include <stdint.h> | |
#include <stdio.h> | |
#include <stdlib.h> | |
#include <string.h> | |
#include <fcntl.h> | |
#include <limits.h> | |
#include <sys/stat.h> | |
#include <unistd.h> | |
typedef struct KV | |
{ | |
char* dir; | |
} KV; | |
bool | |
KV_Open(KV* kv, const char* dir) | |
{ | |
struct stat st; | |
if (stat(dir, &st) != 0 || !S_ISDIR(st.st_mode)) { | |
return false; | |
} | |
kv->dir = strdup(dir); | |
return true; | |
} | |
bool | |
KV_Close(KV* kv) | |
{ | |
free(kv->dir); | |
return true; | |
} | |
ssize_t | |
KV_Load(KV* kv, const char* key, uint8_t* buffer, size_t limit) | |
{ | |
char pathname[PATH_MAX]; | |
int res = snprintf(pathname, sizeof(pathname), "%s/%s", kv->dir, key); | |
if (res < 0 || res >= (int)sizeof(pathname)) { | |
return -1; | |
} | |
int fd = open(pathname, O_RDONLY); | |
if (fd < 0) { | |
return -1; | |
} | |
ssize_t size = read(fd, buffer, limit); | |
close(fd); | |
return size; | |
} | |
bool | |
KV_Save(KV* kv, const char* key, const uint8_t* value, size_t size) | |
{ | |
char pathname[PATH_MAX]; | |
int res = snprintf(pathname, sizeof(pathname), "%s/%s", kv->dir, key); | |
if (res < 0 || res >= (int)sizeof(pathname)) { | |
return false; | |
} | |
int fd = open(pathname, O_WRONLY | O_CREAT, 0644); | |
if (fd < 0) { | |
return false; | |
} | |
ssize_t written = write(fd, value, size); | |
close(fd); | |
return (size_t)written == size; | |
} | |
bool | |
KV_Delete(KV* kv, const char* key) | |
{ | |
char pathname[PATH_MAX]; | |
int res = snprintf(pathname, sizeof(pathname), "%s/%s", kv->dir, key); | |
if (res < 0 || res >= (int)sizeof(pathname)) { | |
return false; | |
} | |
return unlink(pathname) == 0; | |
} | |
int | |
main() | |
{ | |
KV kv; | |
if (!KV_Open(&kv, "/tmp")) { | |
fprintf(stderr, "KV_Open error\n"); | |
return 1; | |
} | |
const char* key = "yoursunny"; | |
uint8_t value[] = { 0x61, 0x77, 0x65, 0x73, 0x6F, 0x6D, 0x65 }; | |
if (!KV_Save(&kv, key, value, sizeof(value))) { | |
fprintf(stderr, "KV_Save error\n"); | |
return 1; | |
} | |
char buffer[16]; | |
ssize_t size = KV_Load(&kv, key, (uint8_t*)buffer, sizeof(buffer) - 1); | |
if (size < 0) { | |
fprintf(stderr, "KV_Load error\n"); | |
return 1; | |
} | |
buffer[size] = '\0'; | |
printf("%s = %s\n", key, buffer); | |
if (!KV_Delete(&kv, key)) { | |
fprintf(stderr, "KV_Delete error\n"); | |
return 1; | |
} | |
if (!KV_Close(&kv)) { | |
fprintf(stderr, "KV_Close error\n"); | |
return 1; | |
} | |
return 0; | |
} |
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#define _POSIX_C_SOURCE 200809L | |
#include <stdbool.h> | |
#include <stdint.h> | |
#include <stdio.h> | |
#include <stdlib.h> | |
#include <string.h> | |
#include <fcntl.h> | |
#include <limits.h> | |
#include <sys/stat.h> | |
#include <unistd.h> | |
typedef struct KV | |
{ | |
int dirfd; | |
} KV; | |
bool | |
KV_Open(KV* kv, const char* dir) | |
{ | |
kv->dirfd = open(dir, O_RDONLY | O_DIRECTORY); | |
return kv->dirfd >= 0; | |
} | |
bool | |
KV_Close(KV* kv) | |
{ | |
close(kv->dirfd); | |
return true; | |
} | |
ssize_t | |
KV_Load(KV* kv, const char* key, uint8_t* buffer, size_t limit) | |
{ | |
int fd = openat(kv->dirfd, key, O_RDONLY); | |
if (fd < 0) { | |
return false; | |
} | |
ssize_t size = read(fd, buffer, limit); | |
close(fd); | |
return size; | |
} | |
bool | |
KV_Save(KV* kv, const char* key, const uint8_t* value, size_t size) | |
{ | |
int fd = openat(kv->dirfd, key, O_WRONLY | O_CREAT, 0644); | |
if (fd < 0) { | |
return false; | |
} | |
ssize_t written = write(fd, value, size); | |
close(fd); | |
return (size_t)written == size; | |
} | |
bool | |
KV_Delete(KV* kv, const char* key) | |
{ | |
return unlinkat(kv->dirfd, key, 0) == 0; | |
} | |
int | |
main() | |
{ | |
KV kv; | |
if (!KV_Open(&kv, "/tmp")) { | |
fprintf(stderr, "KV_Open error\n"); | |
return 1; | |
} | |
const char* key = "yoursunny"; | |
uint8_t value[] = { 0x61, 0x77, 0x65, 0x73, 0x6F, 0x6D, 0x65 }; | |
if (!KV_Save(&kv, key, value, sizeof(value))) { | |
fprintf(stderr, "KV_Save error\n"); | |
return 1; | |
} | |
char buffer[16]; | |
ssize_t size = KV_Load(&kv, key, (uint8_t*)buffer, sizeof(buffer) - 1); | |
if (size < 0) { | |
fprintf(stderr, "KV_Load error\n"); | |
return 1; | |
} | |
buffer[size] = '\0'; | |
printf("%s = %s\n", key, buffer); | |
if (!KV_Delete(&kv, key)) { | |
fprintf(stderr, "KV_Delete error\n"); | |
return 1; | |
} | |
if (!KV_Close(&kv)) { | |
fprintf(stderr, "KV_Close error\n"); | |
return 1; | |
} | |
return 0; | |
} |
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