On Sun, 27 Jan 2002, Rein Klazes wrote:
> You still need ftruncate in case the file has to shrink. To do that
> without ftruncate takes a lot more work then an lseek and a write.
>
> Rein.
>
Right. I meant sort of like this. Unfortunately I haven't an app that
does this, to be sure I have it right.
Changelog
server : file.c
Lawson Whitney <lawson_whitney@juno.com>
Rein Klazes <rklazes@xs4all.nl>
Guy Albertelli <galberte@neo.lrun.com>
Do not rely on ftruncate to grow a file. It may refuse or fail
to do so. (eg with vfat filesystem under Linux)
diff -urN was/server/file.c is/server/file.c
--- was/server/file.c Tue Jan 22 20:57:40 2002
+++ is/server/file.c Sun Jan 27 15:52:51 2002
@@ -456,6 +456,28 @@
return 1;
}
+/* wrapper around ftruncate:
+ * ftruncate may fail to grow the size of a file with some OS and filesystem
+ * combinations. Linux and vfat/fat is one example. To work around this do
+ * a write to grow the file to the desired length.
+ */
+static int _ftruncate ( int fd, off_t length)
+{
+ struct stat st;
+ int ret_errno;
+ char buf[1]={'\0'};
+ ret_errno = errno;
+ if( fstat( fd, &st ) == -1) return -1;
+ errno = ret_errno;
+ /* ftruncate() shouldn't fail when requested to shrink the file */
+ if( st.st_size >= length ) return ftruncate( fd, length);
+ /* file pointer is at the requested size */
+ if( lseek( fd, -1, SEEK_CUR) == -1) return -1;
+ /* write one byte, filepointer is back at the orig. position. */
+ if( write( fd, &buf, 1) == -1) return -1;
+ return 0;
+}
+
static int truncate_file( handle_t handle )
{
struct file *file;
@@ -464,7 +486,7 @@
if (!(file = get_file_obj( current->process, handle, GENERIC_WRITE )))
return 0;
if (((result = lseek( file->obj.fd, 0, SEEK_CUR )) == -1) ||
- (ftruncate( file->obj.fd, result ) == -1))
+ (_ftruncate( file->obj.fd, result ) == -1))
{
file_set_error();
release_object( file );
