[Bug 219] New: O_DIRECT io no longer works when the available data size is less than the underlying block-device size?

[bugzilla-daemon@xxxxxxxxxxx]

http://oss.sgi.com/bugzilla/show_bug.cgi?id=219

           Summary: O_DIRECT io no longer works when the available data size
                    is less than the underlying block-device size?
           Product: Linux XFS
           Version: unspecified
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: Medium
         Component: XFS kernel code
        AssignedTo: xfs-master@xxxxxxxxxxx
        ReportedBy: cw@xxxxxxxx


this occurs linux-2.5.60; 2.4.x (from oss' CVS) works as expected

under 2.4.x i am able to read a 1 byte file O_DIRECT; 2.5.60 fails when doing 
this

testing fs-block-sized (well, == page size, really) reads with a 5k file under
2.4.x shows i can read the first block then a partial for the second block (as
expected)

under 2.5.60 the first block read correctly, the second barfs

--------- snip snip --------- source code ---------
#define _GNU_SOURCE

#include <unistd.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
    int h;
    int ps;
    char *buf;
    ssize_t n;

    ps = getpagesize();
    if (!(buf = valloc(ps)))
        return 1;
    if ((h = open("od.c", O_RDONLY|O_DIRECT)) < 0)
        return 1;
    do {
        n = read(h, buf, ps);
        if (n == -1) {
            perror("read");
            break;
        }
        printf("read %d bytes\n", n);
    } while(n);

    close(h);

    return 0;
}
-------------- snip snip -------- scissor party ----------

results (not a 5k file as mentioned above, s/od.c/a.out/ for that):

cw:0@tapu(cw)$ uname -r
2.4.20-cw2
cw:0@tapu(cw)$ gcc -Wall od.c
cw:0@tapu(cw)$ ./a.out 
read 503 bytes
read 0 bytes
cw:0@tapu(cw)$ 

and

charon:~% uname -r
2.5.60
charon:~% gcc -Wall od.c
charon:~% ./a.out 
read: Invalid argument



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