minix/lib/other/vectorio.c

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2010-01-08 14:40:34 +01:00
#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/uio.h>
#include <unistd.h>
#define VECTORIO_READ 1
#define VECTORIO_WRITE 2
#define MIN(x, y) (((x) < (y)) ? (x) : (y))
static ssize_t vectorio_buffer(int fildes, const struct iovec *iov,
int iovcnt, int readwrite, ssize_t totallen)
{
char *buffer;
int iovidx, errno_saved;
ssize_t copied, len, r;
/* allocate buffer */
buffer = (char *) malloc(totallen);
if (!buffer)
return -1;
/* perform the actual read/write for the entire buffer */
switch (readwrite)
{
case VECTORIO_READ:
/* first read, then copy buffers (only part read) */
r = read(fildes, buffer, totallen);
copied = 0;
iovidx = 0;
while (copied < r)
{
assert(iovidx < iovcnt);
len = MIN(r - copied, iov[iovidx].iov_len);
memcpy(iov[iovidx++].iov_base, buffer + copied, len);
copied += len;
}
assert(r < 0 || r == copied);
break;
case VECTORIO_WRITE:
/* first copy buffers, then write */
copied = 0;
for (iovidx = 0; iovidx < iovcnt; iovidx++)
{
memcpy(buffer + copied, iov[iovidx].iov_base,
iov[iovidx].iov_len);
copied += iov[iovidx].iov_len;
}
assert(copied == totallen);
r = write(fildes, buffer, totallen);
break;
default:
assert(0);
errno = EINVAL;
r = -1;
}
/* free the buffer, keeping errno unchanged */
errno_saved = errno;
free(buffer);
errno = errno_saved;
return r;
}
static ssize_t vectorio(int fildes, const struct iovec *iov,
int iovcnt, int readwrite)
{
int i;
struct stat statbuf;
ssize_t totallen;
/* parameter sanity checks */
if (iovcnt > IOV_MAX)
{
errno = EINVAL;
return -1;
}
totallen = 0;
for (i = 0; i < iovcnt; i++)
{
/* don't read/write anything in case of possible overflow */
if ((ssize_t) (totallen + iov[i].iov_len) < totallen)
{
errno = EINVAL;
return -1;
}
totallen += iov[i].iov_len;
/* report on NULL pointers */
if (iov[i].iov_len && !iov[i].iov_base)
{
errno = EFAULT;
return -1;
}
}
/* anything to do? */
if (totallen == 0)
return 0;
/*
* there aught to be a system call here; instead we use an intermediate
* buffer; this is preferred over multiple read/write calls because
* this function has to be atomic
*/
return vectorio_buffer(fildes, iov, iovcnt, readwrite, totallen);
}
ssize_t readv(int fildes, const struct iovec *iov, int iovcnt)
{
return vectorio(fildes, iov, iovcnt, VECTORIO_READ);
}
ssize_t writev(int fildes, const struct iovec *iov, int iovcnt)
{
return vectorio(fildes, iov, iovcnt, VECTORIO_WRITE);
}