Re: read failed EINVAL with O_DIRECT flag

[Yves Crespin <crespin.quartz@wanadoo.fr>]

I've got compilation error when I call vmalloc() from a user program 
(w/o defined __KENEL).
How can I obtains an buffer alignement from a "user program" ?

Randy.Dunlap wrote:

>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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