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?
execve("./testopen", ["./testopen"], [/* 30 vars */]) = 0
uname({sys="Linux", node="urca", ...}) = 0
brk(0) = 0x80497fc
open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or
directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=57677, ...}) = 0
old_mmap(NULL, 57677, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40012000
close(3) = 0
open("/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0]Z\1\000"...,
1024) = 1024
fstat64(3, {st_mode=S_IFREG|0755, st_size=1102984, ...}) = 0
old_mmap(NULL, 1112740, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) =
0x40021000
mprotect(0x40129000, 31396, PROT_NONE) = 0
old_mmap(0x40129000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
3, 0x107000) = 0x40129000
old_mmap(0x4012f000, 6820, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x4012f000
close(3) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x40131000
munmap(0x40012000, 57677) = 0
open("/var/tmp/testopen.txt", O_RDONLY|O_DIRECT) = 3
brk(0) = 0x80497fc
brk(0x804c7fc) = 0x804c7fc
brk(0) = 0x804c7fc
brk(0x804d000) = 0x804d000
read(3, "", 4096) = 0
fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 4), ...}) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x40012000
write(1, "0 bytes read from file.\n", 240 bytes read from file.
) = 24
close(3) = 0
write(1, "Message: ", 9Message: ) = 9
munmap(0x40012000, 4096) = 0
exit_group(0) = ?
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.
>
>
>
> --cw
-- Bruno Diniz de Paula <diniz@cs.rutgers.edu> Rutgers University
- 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/
This archive was generated by hypermail 2b29 : Sat Feb 15 2003 - 22:00:45 EST