read failed EINVAL with O_DIRECT flag

read failed EINVAL with O_DIRECT flag

[Yves Crespin]

Hello,

Using O_DIRECT flag, read() failed and errno is EINVAL.
kernel 2.4.22
Filesystem Ext3 mount on /home
What's wrong ?
Thanks

Yves Crespin

#gcc -Wall -D_GNU_SOURCE direct.c -o direct
#cp direct d
#./direct d
#open failed [d] 040402 0666 errno 22
#

/* --- 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;
}
/* --- end code --- */

Re: read failed EINVAL with O_DIRECT flag

[Randy.Dunlap]

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

Re: read failed EINVAL with O_DIRECT flag

[Yves Crespin]

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
>-
>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>Please read the FAQ at  http://www.tux.org/lkml/
>
>
>  
>

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

Re: read failed EINVAL with O_DIRECT flag

[Yves Crespin]

 >| 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)?

Well ... either with malloc() and alignement or posix_memalign(),
read() still failed!
My read buffer is in user space, so it's copy to kernel space.
Inside the read() call, it's the kernel buffer which must be aligned?

 >
 >| >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;
    int        openFlags;
    int        fd;
    int        nb;
    off_t        size;
    blksize_t    blksize;
    off_t        offset;

    if (argc!=2){
        printf("Missing file name\n");
        exit(2);
    }
    printf("[%s]\n",argv[1]);
    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);
    }
    blksize = sbuf.st_blksize;
    size = sbuf.st_size;
    nb = posix_memalign((void **)&buf,blksize,size);
    if (nb!=0){
        printf("posix_memalign blksize %lu size %lu failed 
%d\n",blksize,size,nb);
        exit(3);
    }
#if 0
    free(buf);
    buf = malloc(2*blksize);
#endif
    printf("direct: buf %p buf & (blksize-1) %lu\n",buf,(unsigned 
long)buf & (unsigned long)(blksize-1));
    for (offset=0;offset<blksize;offset++){
        if (!((unsigned long)(buf+offset) & (unsigned long)(blksize-1))){
            printf("offset: buf %p buf & (blksize-1) %lu offset 
%lu\n",buf+offset,(unsigned long)(buf+offset) & (unsigned 
long)(blksize-1),offset);
            break;
        }
    }
    printf("align:  buf %p buf & (blksize-1) %lu\n",buf+offset,(unsigned 
long)(buf+offset) & (unsigned long)(blksize-1));
    nb = read(fd,buf+offset,blksize);
    if (nb != blksize){
        printf("read failed fd %d buf %p buf & (blksize-1) %lu blksize 
%lu size %lu nb %d errno %d\n",
                fd,buf+offset,(unsigned long)(buf+offset) & (unsigned 
long)(blksize-1),
                (unsigned long)blksize,size,nb,errno);
        exit(1);
    }
    if (close(fd)){
        printf("close failed\n");
        exit(1);
    }
    free(buf);
    return 0;
}
/* --- end code --- */

Re: read failed EINVAL with O_DIRECT flag

[Randy.Dunlap]

On Wed, 13 Apr 2005 15:15:47 +0200 Yves Crespin wrote:

| 
|  >| 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)?
| 
| Well ... either with malloc() and alignement or posix_memalign(),
| read() still failed!
| My read buffer is in user space, so it's copy to kernel space.
| Inside the read() call, it's the kernel buffer which must be aligned?

No, it's the userspace buffer.  However...
the check below isn't even reached for ext3 filesystems in
Linux 2.4.  I.e., 2.4 does not support O_DIRECT for ext3fs.
mount a partition as -t ext2 and your (modified) program
works fine.  Or use 2.6.current...

Sorry to mislead you somewhat, although you do still need
the buffer alignment fixes.


|  >| >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().


---
~Randy