Re: [LTP] [PATCH/RFC] aiodio: make read_sparse use same mode as writers

[chrubis@suse.cz]

Hi!
> > I've looked at the test and what it does is:
> > 
> > 1. create file and make sure it's empty
> > 2. truncate it to defined size
> > 3. parent starts writing zeroes to it with O_DIRECT
> > 4. childs reads it and expect to get zeroes at any time
> 
> Hi,
> 
> That looks correct, here's an strace excerpt:
> 
> 04:05:38.464923 open("/tmp/dio_sparse", O_RDWR|O_CREAT|O_EXCL|O_DIRECT, 0600) = 5
> 04:05:38.464985 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f7583c0da10) = 22242
> Process 22242 attached
> [pid 22242] 04:05:38.465142 open("/tmp/dio_sparse", O_RDONLY) = 6
> [pid 22234] 04:05:38.465369 ftruncate(5, 2048 <unfinished ...>
> [pid 22242] 04:05:38.465400 lseek(6, 0, SEEK_SET <unfinished ...>
> [pid 22234] 04:05:38.465458 <... ftruncate resumed> ) = 0
> [pid 22242] 04:05:38.465474 <... lseek resumed> ) = 0
> [pid 22234] 04:05:38.465509 write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 4096 <unfinished ...>
> [pid 22242] 04:05:38.465540 read(6, "04:05:14.921896 execve(\"./dio_sp"..., 4096) = 2048
> [pid 22242] 04:05:38.482378 fstat(1, {st_mode=S_IFREG|0644, st_size=14502, ...}) = 0
> [pid 22242] 04:05:38.482419 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f7583c18000
> [pid 22242] 04:05:38.482473 write(1, "dummy not zero at 0, 0x30\n", 26dummy not zero at 0, 0x30
> ) = 26

So the read gets something that looks like part of the strace? How is
that even possible?

> > This should really work and I've been told by our filesystem guy that
> > this really looks like bug in the kernel (assuming that I haven't
> > overlooked something in the test source).
> 
> Do you know about any doc/source that says why it should work?
> In my search I only came across that man page, which seems to go in
> opposite way.

I simply asked Jan Kara.

-- 
Cyril Hrubis
chrubis@suse.cz

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