Re: [ANNOUNCE] Native Linux KVM tool v2

From: Pekka Enberg
Date: Thu Jun 16 2011 - 06:03:04 EST

On Thu, Jun 16, 2011 at 12:48 PM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> You also missed:
> " This system call does not flush disk write caches and thus does not
>  provide any data integrity on systems with volatile disk write
>  caches."
> so it's not safe if you either have a cache, or are using btrfs, or
> are using a sparse image, or are using an image preallocated using
> fallocate/posix_fallocate.

Uh-oh. Someone needs to apply this patch to sync_file_range():

diff --git a/fs/sync.c b/fs/sync.c
index ba76b96..32078aa 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -277,6 +277,8 @@ SYSCALL_DEFINE(sync_file_range)(int fd, loff_t
offset, loff_t nbytes,
int fput_needed;
umode_t i_mode;

+ WARN_ONCE(1, "when this breaks, you get to keep both pieces");
ret = -EINVAL;
if (flags & ~VALID_FLAGS)
goto out;

>> What's the right thing to do here? Is fdatasync() sufficient?
> Yes.

We'll fix that up. Thanks Christoph!

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