RE: Direct I/O questions
- From: "Magni Fabrizio" <Fabrizio.Magni@xxxxxxxxx>
- To: <james.p.kramer@xxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 10 Dec 2004 09:17:52 +0100
Hi James,
I can confirm you two things:
linux support direct i/o (with o_direct),
SLES9 seems to have o_direct broken.
I'm subbmitting the program I'm using to test.
It works on SLES8, debian with 2.6.x kernels, ubuntu on several
filesystems: ext2, ext3, xfs, reiserfs.
If I manage to find a fedora I'll go on testing.
I fear something is not working as expected in SuSE 2.6.5-7.97 kernel.
Regards
Fabrizio
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <asm/fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
int main(int argc, char *argv[])
{
char *message;
int fd =3D open("/tmp/xxx", O_RDONLY|O_DIRECT);
int len, pagesize =3D getpagesize();
posix_memalign((void **)&message, pagesize, pagesize);
if(fd < 0) {
printf("Unable to open file, errno is %d.\n", errno);
} else {
if((len =3D read(fd, message, pagesize)) < 0) {
perror("read");
} else {
printf("%d bytes read from file.\n", len);
printf("Message: %s", message);
}
}
close(fd);
}
> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx=20
> [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Kramer, James P.
> Sent: Wednesday, December 08, 2004 9:59 PM
> To: oracle-l@xxxxxxxxxxxxx
> Subject: Direct I/O questions
>=20
>=20
> > First things first, this isn't an oracle question but=20
> rather a series =3D
> of questions based on a previous message on the oracle-l=20
> list. If you =3D
> think I should post it on a different list please let me know=20
> which one.
> >=3D20
> > The message I am talking about can be found here.
> > //www.freelists.org/archives/oracle-l/02-2004/msg03007.html
> >=3D20
> > Also, I am new to the Linux world (just thought I'd let you=20
> know what =3D
> kind of a guy your dealing with...newbie).
> >=3D20
> > Here is the following information about our Linux server.
> >=3D20
> > We are running SUSE LINUX Enterprise Server 9. From the=20
> files located =3D
> in /usr/src, the version is 2.6.5-7.97. I'm not sure how=20
> else to get =3D
> the version.
> > There are 8 IA64 processors.
> >=3D20
> > I have been researching ways to get direct I/O to work on=20
> our Linux =3D
> machine when I stumbled across the above message. Within the=20
> message =3D
> was a small code example that tested direct I/O. I tried=20
> this code out =3D
> to see if it would work. I could not get the code to compile=20
> as is. =3D
> With some modifying (changed the headers), I was able to get it to =3D
> compile but the direct I/O read kept giving me EINVAL (Invalid =3D
> Argument).
> >=3D20
> > Here is the modified code that I used.
> >=3D20
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <sys/types.h>
> > #include <sys/stat.h>
> > #include <errno.h>
> > #include <string.h>
> > #include <fcntl.h>
> > #include <unistd.h>
> > #define BUFFSIZE 65536
> > #define ALIGN 4096
> >=3D20
> > int main()=3D20
> > {=3D20
> > char *buff;
> > int stat1=3D3D0,stat2=3D3D0,stat3=3D3D0;
> > int fd1=3D3D0,fd2=3D3D0;
> > if (stat3=3D3Dposix_memalign((void **)&buff,ALIGN,BUFFSIZE)) {
> > fprintf(stderr,"ALIGN ERR:%s\n",strerror(stat3));
> > exit(0);
> > }
> >=3D20
> > fd1=3D3Dopen("/home/rrd/workspace/IORead.txt", =3D
> O_RDONLY|O_DIRECT,S_IRWXU);
> >=3D20
> > =3D
> fd2=3D3Dopen("/home/rrd/workspace/IOWrite.txt",O_CREAT|O_WRONLY|
> O_DIRECT,S_=3D
> IRWXU);
> > while(stat1=3D3Dread(fd1,buff,BUFFSIZE)) {
> > if (errno) {
> > fprintf(stderr,"READ ERR:%s\n",strerror(errno));
> > exit(0);
> > }
> > stat2=3D3Dwrite(fd2,buff,(unsigned) stat1);
> > if (errno) {
> > fprintf(stderr,"WRITE ERR:%s\n",strerror(errno));
> > exit(0);
> > }
> > }
> > close(fd1);
> > close(fd2);
> > =3D20
> > return 0;
> > }
> >=3D20
> > Also, is there a programmatic way of retrieving the alignment and =
=3D
> block size? I have seen the fcntl call for F_DIOINFO. =20
> However, I have =3D
> read articles that Linux doesn't have this. Instead one must=20
> use ioctl =3D
> with XFS_IOC_DIOINFO. When I do a search in /usr/, the only=20
> *DIOINFO =3D
> that I find is in xfs_fs.h. When I try calling this=20
> function, I get an =3D
> error and from what I gather it is because the file doesn't=20
> support this =3D
> type of ioctl. Does this mean I am missing some feature?
> >=3D20
> > I have been searching Google about direct I/O and have come across =
=3D
> countless articles that seem to contradict one another. Some=20
> articles =3D
> say that Linux doesn't support O_DIRECT and that you need to convert =
=3D
> your file system to XFS and use those libraries. Others say it does =
=3D
> support it. From the example above it seems it doesn't support it. =
=3D
> What must be done to the file system (if anything) to get=20
> direct I/O to =3D
> work? Do I need to convert to XFS?
> >=3D20
> > Could it be that I'm using the wrong libraries? How can I=20
> find out =3D
> what libraries it is using?
> >=3D20
> > Is there anything I should look at on the server to make=20
> sure I have =3D
> the most up-to-date stuff? Any other ideas on how I should proceed?
> >=3D20
> > Any help would greatly be appreciated.
> >=3D20
> > James Kramer
> >=3D20
> >=3D20
> > THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE =3D
> PROPRIETARY MATERIAL and is thus for use only by the intended=20
> recipient. =3D
> If you received this in error, please contact the sender and=20
> delete the =3D
> e-mail and its attachments from all computers.=3D20
> >=3D20
> >=3D20
> --
> //www.freelists.org/webpage/oracle-l
>=20
--
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