On 12 Feb 2003 18:22:35 -0500
Bruno Diniz de Paula <diniz@cs.rutgers.edu> wrote:
| Just to complete the information, I am trying to read a file with 5
| bytes, and here is the piece of code I am using:
|
| char *message;
| int fd = open("/var/tmp/testopen.txt", O_RDONLY|O_DIRECT);
| int len, pagesize = getpagesize();
|
| posix_memalign((void **)&message, pagesize, pagesize);
| if(fd < 0) {
| printf("Unable to open file, errno is %d.\n", errno);
| } else {
| if((len = read(fd, message, pagesize)) < 0) {
| perror("read");
| } else {
| printf("%d bytes read from file.\n", len);
| printf("Message: %s", message);
| }
| }
| close(fd);
|
| Thanks,
|
| Bruno.
|
| On Wed, 2003-02-12 at 18:02, Bruno Diniz de Paula wrote:
| > On Wed, 2003-02-12 at 17:42, Chris Wedgwood wrote:
| > > On Wed, Feb 12, 2003 at 05:29:52PM -0500, Bruno Diniz de Paula wrote:
| > >
| > > > But I am using multiples of page size in both buffer alignment and
| > > > buffer size (2nd and 3rd parameters of read). The issue is that
| > > > when I try to read files with sizes that are NOT multiples of block
| > > > size (and therefore also not multiples of page size), the read
| > > > syscall returns 0, with no errors.
| > >
| > > What filesystem?
| >
| > ext2.
| >
| > >
| > > Can you send an strace of this occurring?
| >
[strace snipped]
| >
| > Thanks a lot,
| >
| > Bruno.
| >
| > >
| > > > So the question remains, am I able to read just files whose size is
| > > > a multiple of block size?
| > >
| > > No.
| > >
| > > You ideally should be able to read any length file with O_DIRECT.
| > > Even a 1-byte file.
Here's what I get using Bruno's and cw's (od) programs:
2.4.8|2.4.20 2.4.20 2.5.54
ext2 ext3 ext2|ext3
==== ==== =========
od: read 0 bytes read: Inv. arg. read: Inv. arg.
bruno: 0 bytes read read: Inv. arg. read: Inv. arg.
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