smk@axiom.UUCP (Steven M. Kramer) (06/22/85)
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
/*
* This mimicks a 4.2BSD system call. Here, we just make it
* a lil ol' routine. It expects a file descriptor, the NEW
* size to truncate to, and the file name (which we use but 4.2
* doesn't). What we do simply is copy size bytes to a temporary
* file, truncate the original file to zero (which we CAN do), and
* then copy the second file back to the first.
*
* Steve Kramer Copyright 1/18/84
* Not to be used for profit without author's permission.
* May be otherwise redistributed.
*/
ftruncate(fr, size)
int fr;
long size;
{
extern char *mktemp();
struct stat stat_buf;
char *tname;
register int tf;
register int s, n;
long int new_size;
char buf[BUFSIZ];
/*
* Get a temporary file to copy to.
*/
tname = mktemp("/tmp/sXXXXXX");
close(creat(tname, 0600));
tf = open(tname, 2);
if(tf < 0) {
unlink(tname);
return (-1);
}
/*
* Copy the original to the temporary file. Do it in increments
* of BUFSIZ for efficiency.
*/
new_size = size;
lseek(fr, (long)0, 0);
while(new_size != 0) {
s = BUFSIZ;
if(new_size < BUFSIZ)
s = new_size;
n = read(fr, buf, s);
if(n != s) {
close(tf);
unlink(tname);
return(-1);
}
n = write(tf, buf, s);
if(n != s) {
close(tf);
unlink(tname);
return(-1);
}
new_size -= s;
}
/*
* Truncate the original file no that the information is
* stuck tightly away in the temporary.
*/
lseek(fr, (long)0, 0);
lseek(tf, (long)0, 0);
if (fstat (fr, &stat_buf) == 0)
close(creat(name, stat_buf.st_mode & 0777));
else
close(creat(name, 0755));
/*
* Now, copy back.
*/
new_size = size;
while(new_size != 0) {
s = BUFSIZ;
if(new_size < BUFSIZ)
s = new_size;
n = read(tf, buf, s);
if(n != s) {
close (tf);
unlink(tname);
return(-1);
}
n = write(fr, buf, s);
if(n != s) {
close (tf);
unlink(tname);
return(-1);
}
new_size -= s;
}
/*
* Close and remove the temporary file. It's no longer needed.
*/
close(tf);
unlink(tname);
return(0);
}
--
--steve kramer
{allegra,genrad,ihnp4,utzoo,philabs,uw-beaver}!linus!axiom!smk (UUCP)
linus!axiom!smk@mitre-bedford (MIL)