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libjio/bindings/preload/libjio_preload.c  view on Meta::CPAN

/*
 * libjio C preloader
 * Alberto Bertogli (albertito@blitiri.com.ar)
 *
 * This generates a shared object that, when prelinked, can be used to make an
 * existing application to use libjio for UNIX I/O.
 * It's not nice or pretty, and does some nasty tricks to work both with and
 * without LFS. I don't think it builds or works without glibc.
 */


#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/uio.h>
#include <dlfcn.h>

/* we don't build this with LFS, however, it's essential that the proper
 * environment is set for libjio's loading; otherwise we would mess the ABI
 * up */
typedef long long off64_t;
#define _FILE_OFFSET_BITS 64
#define off_t off64_t
#include <libjio.h>
#undef off_t
#undef _FILE_OFFSET_BITS


/* maximum number of simultaneous open file descriptors we support */
#define MAXFD (4096 * 2)

/* recursion counter, per-thread */
static int __thread called = 0;


/* C library functions, filled via the dynamic loader */
static void *libc;

static int (*c_open)(const char *pathname, int flags, mode_t mode);
static int (*c_open64)(const char *pathname, int flags, mode_t mode);
static int (*c_close)(int fd);
static int (*c_unlink)(const char *pathname);
static ssize_t (*c_read)(int fd, void *buf, size_t count);
static ssize_t (*c_pread)(int fd, void *buf, size_t count, off_t offset);
static ssize_t (*c_pread64)(int fd, void *buf, size_t count, off64_t offset);
static ssize_t (*c_readv)(int fd, const struct iovec *vector, int count);
static ssize_t (*c_write)(int fd, const void *buf, size_t count);
static ssize_t (*c_pwrite)(int fd, const void *buf, size_t count, off_t offset);
static ssize_t (*c_pwrite64)(int fd, const void *buf, size_t count, off64_t offset);
static ssize_t (*c_writev)(int fd, const struct iovec *vector, int count);
static int (*c_ftruncate)(int fd, off_t length);
static int (*c_ftruncate64)(int fd, off64_t length);
static off_t (*c_lseek)(int fd, off_t offset, int whence);
static off64_t (*c_lseek64)(int fd, off64_t offset, int whence);
static int (*c_fsync)(int fd);
static int (*c_dup)(int oldfd);
static int (*c_dup2)(int oldfd, int newfd);


/* file descriptor table, to translate fds to jfs */
struct fd_entry {
	int fd;
	unsigned int *refcount;
	jfs_t *fs;
	pthread_mutex_t lock;
};
static struct fd_entry fd_table[MAXFD];

/* useful macros, mostly for debugging purposes */
#if 1
	#define rec_inc() do { called++; } while(0)
	#define rec_dec() do { called--; } while(0)
	#define printd(...) do { } while(0)

#else
	/* debug variants */

	#define rec_inc()				\
		do {					\
			called++;			\
			fprintf(stderr, "I: %d\n", called); \
			fflush(stderr);			\
		} while (0)

	#define rec_dec()				\
		do {					\
			called--;			\
			fprintf(stderr, "D: %d\n", called); \
			fflush(stderr);			\
		} while (0)

	#define printd(...)				\
		do {					\
			if (called)			\
				fprintf(stderr, "\t");	\
			called++;			\
			fprintf(stderr, "%5.5d ", getpid()); \
			fprintf(stderr, "%s(): ", __FUNCTION__ ); \
			fprintf(stderr, __VA_ARGS__);	\
			fflush(stderr);			\
			called--;			\
		} while(0)
#endif


/* functions used to lock fds from the table; they do boundary checks so we
 * catch out of bounds accesses */
static inline int fd_lock(int fd)
{
	int r;

	if (fd < 0 || fd >= MAXFD) {
		printd("locking out of bounds fd %d\n", fd);
		return 0;
	}
	//printd("L %d\n", fd);
	r = pthread_mutex_lock(&(fd_table[fd].lock));
	//printd("OK %d\n", fd);
	return !r;
}

static inline int fd_unlock(int fd)
{
	int r;

	if (fd < 0 || fd >= MAXFD) {
		printd("unlocking out of bounds fd %d\n", fd);
		return 0;
	}
	//printd("U %d\n", fd);
	r = pthread_mutex_unlock(&(fd_table[fd].lock));
	//printd("OK %d\n", fd);
	return !r;
}


/*
 * library intialization
 */

static int __attribute__((constructor)) init(void)
{
	int i;
	pthread_mutexattr_t attr;

	printd("starting\n");

	/* initialize fd_table */
	pthread_mutexattr_init(&attr);
	pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_NORMAL);
	for (i = 0; i < MAXFD; i++) {
		fd_table[i].fd = -1;
		fd_table[i].fs = NULL;
		pthread_mutex_init(&(fd_table[i].lock), &attr);
	}
	pthread_mutexattr_destroy(&attr);

	/* dynamically load the C library */
	libc = dlopen("libc.so.6", RTLD_NOW);
	if (libc == NULL) {
		printd("Error loading libc: %s\n", dlerror());
		return 0;
	}

	/* load symbols from the C library */
	#define libc_load(F) c_##F = dlsym(libc, #F)
	libc_load(open);
	libc_load(open64);
	libc_load(close);
	libc_load(unlink);
	libc_load(read);
	libc_load(pread);
	libc_load(pread64);
	libc_load(readv);
	libc_load(write);
	libc_load(pwrite);
	libc_load(pwrite64);
	libc_load(writev);
	libc_load(ftruncate);
	libc_load(ftruncate64);
	libc_load(lseek);
	libc_load(lseek64);
	libc_load(fsync);
	libc_load(dup);
	libc_load(dup2);

	printd("done\n");
	return 1;
}

/*
 * wrappers
 */

int open(const char *pathname, int flags, ...)
{
	int r, fd;
	jfs_t *fs;
	mode_t mode;
	struct stat st;
	va_list l;

	if (flags & O_CREAT) {
		va_start(l, flags);
		mode = va_arg(l, mode_t);
		va_end(l);
	} else {
		/* set it to 0, it's ignored anyway */
		mode = 0;
	}

	if (called) {
		printd("orig (r)\n");
		return (*c_open)(pathname, flags, mode);
	}
	printd("libjio\n");