Re: read failed EINVAL with O_DIRECT flag

[Randy.Dunlap]

On Tue, 12 Apr 2005 18:16:40 +0200 Yves Crespin wrote:

| I've got compilation error when I call vmalloc() from a user program 
| (w/o defined __KENEL).

Where did vmalloc() come from?
I said malloc(), not vmalloc().

| How can I obtains an buffer alignement from a "user program" ?

I actually left that as an exercise (after I did it at home
last night).  Did you read the hint (below)?

| >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().

'man malloc' refers to posix_memalign().  That's not what I
used to test it, but if it works, it should be a good choice.


| 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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