On Mon, 11 Apr 2005 21:14:17 +0200 Yves Crespin wrote:
| Hello,
|
| Using O_DIRECT flag, read() failed and errno is EINVAL.
| kernel 2.4.22
| Filesystem Ext3 mount on /home
| What's wrong ?
| Thanks
In fs/buffer.c, it wants the buffer & the length (size) to be aligned:
function: brw_kiovec()
/*
* First, do some alignment and validity checks
*/
for (i = 0; i < nr; i++) {
iobuf = iovec[i];
if ((iobuf->offset & (size-1)) ||
(iobuf->length & (size-1)))
return -EINVAL;
if (!iobuf->nr_pages)
panic("brw_kiovec: iobuf not initialised");
}
so in your program, malloc() the buf [pointer] (larger than needed)
and then align it to a page boundary and pass that aligned pointer
to read().
| /* --- start code --- */
| #include <stdio.h>
| #include <unistd.h>
| #include <stdlib.h>
| #include <sys/types.h>
| #include <sys/stat.h>
| #include <fcntl.h>
| #include <errno.h>
|
| #define O_BINARY 0
|
| int main(int argc,char *argv[])
| {
| struct stat sbuf;
| char buf[8192];
| int openFlags;
| int fd;
| int nb;
| int size;
|
| if (argc!=2){
| printf("Missing file name\n");
| exit(2);
| }
| openFlags = O_RDWR|O_BINARY|O_NOCTTY;
| openFlags |= O_DIRECT; /* Not POSIX */
| fd = open(argv[1],openFlags,0666);
| if (fd==-1){
| printf("open failed [%s] %#o %#o errno
| %d\n",argv[1],openFlags,0666,errno);
| exit(1);
| }
| if (fstat(fd,&sbuf)<0){
| printf("fstat failed\n");
| exit(1);
| }
| size = sbuf.st_blksize;
| if (size > sizeof(buf)){
| printf("Page size too big\n");
| exit(3);
| }
| if (size > sbuf.st_size){
| printf("File too small\n");
| exit(3);
| }
| nb = read(fd,buf,size);
| if (nb != size){
| printf("read failed fd %d size %d nb %d errno
| %d\n",fd,size,nb,errno);
| exit(1);
| }
| if (close(fd)){
| printf("close failed\n");
| exit(1);
| }
| return 0;
| }
---
~Randy
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