uclibc-ng/libc/sysdeps/linux/common/pread_write.c

/* vi: set sw=4 ts=4: */
/*
 * Copyright (C) 2000-2006 Erik Andersen <andersen@uclibc.org>
 *
 * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
 */
/*
 * Based in part on the files
 *		./sysdeps/unix/sysv/linux/pwrite.c,
 *		./sysdeps/unix/sysv/linux/pread.c,
 *		sysdeps/posix/pread.c
 *		sysdeps/posix/pwrite.c
 * from GNU libc 2.2.5, but reworked considerably...
 */

#include <sys/syscall.h>
#include <unistd.h>
#include <stdint.h>
#include <endian.h>

extern __typeof(pread) __libc_pread;
extern __typeof(pwrite) __libc_pwrite;
#ifdef __UCLIBC_HAS_LFS__
extern __typeof(pread64) __libc_pread64;
extern __typeof(pwrite64) __libc_pwrite64;
#endif

#include <bits/kernel_types.h>

#ifdef __NR_pread

# define __NR___syscall_pread __NR_pread
static __inline__ _syscall5(ssize_t, __syscall_pread, int, fd, void *, buf,
		size_t, count, off_t, offset_hi, off_t, offset_lo);

ssize_t __libc_pread(int fd, void *buf, size_t count, off_t offset)
{
	return __syscall_pread(fd, buf, count, __LONG_LONG_PAIR(offset >> 31, offset));
}
weak_alias(__libc_pread,pread)

# ifdef __UCLIBC_HAS_LFS__
ssize_t __libc_pread64(int fd, void *buf, size_t count, off64_t offset)
{
    uint32_t low = offset & 0xffffffff;
    uint32_t high = offset >> 32;
	return __syscall_pread(fd, buf, count, __LONG_LONG_PAIR(high, low));
}
weak_alias(__libc_pread64,pread64)
# endif /* __UCLIBC_HAS_LFS__  */

#endif /* __NR_pread */

#ifdef __NR_pwrite

# define __NR___syscall_pwrite __NR_pwrite
static __inline__ _syscall5(ssize_t, __syscall_pwrite, int, fd, const void *, buf,
		size_t, count, off_t, offset_hi, off_t, offset_lo);

ssize_t __libc_pwrite(int fd, const void *buf, size_t count, off_t offset)
{
	return __syscall_pwrite(fd, buf, count, __LONG_LONG_PAIR(offset >> 31, offset));
}
weak_alias(__libc_pwrite,pwrite)

# ifdef __UCLIBC_HAS_LFS__
ssize_t __libc_pwrite64(int fd, const void *buf, size_t count, off64_t offset)
{
    uint32_t low = offset & 0xffffffff;
    uint32_t high = offset >> 32;
	return __syscall_pwrite(fd, buf, count, __LONG_LONG_PAIR(high, low));
}
weak_alias(__libc_pwrite64,pwrite64)
# endif /* __UCLIBC_HAS_LFS__  */
#endif /* __NR_pwrite */

#if ! defined __NR_pread || ! defined __NR_pwrite
libc_hidden_proto(read)
libc_hidden_proto(write)
libc_hidden_proto(lseek)

static ssize_t __fake_pread_write(int fd, void *buf,
		size_t count, off_t offset, int do_pwrite)
{
	int save_errno;
	ssize_t result;
	off_t old_offset;

	/* Since we must not change the file pointer preserve the
	 * value so that we can restore it later.  */
	if ((old_offset=lseek(fd, 0, SEEK_CUR)) == (off_t) -1)
		return -1;

	/* Set to wanted position.  */
	if (lseek(fd, offset, SEEK_SET) == (off_t) -1)
		return -1;

	if (do_pwrite == 1) {
		/* Write the data.  */
		result = write(fd, buf, count);
	} else {
		/* Read the data.  */
		result = read(fd, buf, count);
	}

	/* Now we have to restore the position.  If this fails we
	 * have to return this as an error.  */
	save_errno = errno;
	if (lseek(fd, old_offset, SEEK_SET) == (off_t) -1)
	{
		if (result == -1)
			__set_errno(save_errno);
		return -1;
	}
	__set_errno(save_errno);
	return(result);
}

# ifdef __UCLIBC_HAS_LFS__
libc_hidden_proto(lseek64)

static ssize_t __fake_pread_write64(int fd, void *buf,
		size_t count, off64_t offset, int do_pwrite)
{
	int save_errno;
	ssize_t result;
	off64_t old_offset;

	/* Since we must not change the file pointer preserve the
	 * value so that we can restore it later.  */
	if ((old_offset=lseek64(fd, 0, SEEK_CUR)) == (off64_t) -1)
		return -1;

	/* Set to wanted position.  */
	if (lseek64(fd, offset, SEEK_SET) == (off64_t) -1)
		return -1;

	if (do_pwrite == 1) {
		/* Write the data.  */
		result = write(fd, buf, count);
	} else {
		/* Read the data.  */
		result = read(fd, buf, count);
	}

	/* Now we have to restore the position. */
	save_errno = errno;
	if (lseek64(fd, old_offset, SEEK_SET) == (off64_t) -1) {
		if (result == -1)
			__set_errno (save_errno);
		return -1;
	}
	__set_errno (save_errno);
	return result;
}
# endif /* __UCLIBC_HAS_LFS__  */
#endif /*  ! defined __NR_pread || ! defined __NR_pwrite */

#ifndef __NR_pread
ssize_t __libc_pread(int fd, void *buf, size_t count, off_t offset)
{
	return __fake_pread_write(fd, buf, count, offset, 0);
}
weak_alias(__libc_pread,pread)

# ifdef __UCLIBC_HAS_LFS__
ssize_t __libc_pread64(int fd, void *buf, size_t count, off64_t offset)
{
	return __fake_pread_write64(fd, buf, count, offset, 0);
}
weak_alias(__libc_pread64,pread64)
# endif /* __UCLIBC_HAS_LFS__  */
#endif /* ! __NR_pread */

#ifndef __NR_pwrite
ssize_t __libc_pwrite(int fd, const void *buf, size_t count, off_t offset)
{
	/* we won't actually be modifying the buffer,
	 *just cast it to get rid of warnings */
	return __fake_pread_write(fd, (void*)buf, count, offset, 1);
}
weak_alias(__libc_pwrite,pwrite)

# ifdef __UCLIBC_HAS_LFS__
ssize_t __libc_pwrite64(int fd, const void *buf, size_t count, off64_t offset)
{
	return __fake_pread_write64(fd, (void*)buf, count, offset, 1);
}
weak_alias(__libc_pwrite64,pwrite64)
# endif /* __UCLIBC_HAS_LFS__  */
#endif /* ! __NR_pwrite */