On 06/09/2014 01:26 PM, John Muir wrote:
On 2014.06.09, at 9:50 , Maxim Patlasov <mpatla...@parallels.com> wrote:
On 06/06/2014 05:51 PM, John Muir wrote:
On 2014.06.06, at 15:27 , Maxim Patlasov <mpatla...@parallels.com> wrote:
The patch-set resolves the problem by making fuse_release synchronous:
wait for ACK from userspace for FUSE_RELEASE if the feature is ON.
Why not make this feature per-file with a new flag bit in struct fuse_file_info
rather than as a file-system global?
I don't expect a great demand for such a granularity. File-system global
"close_wait" conveys a general user expectation about filesystem behaviour in
distributed environment: if you stopped using a file on given node, whether it means that
the file is immediately accessible from another node.
By user do you mean the end-user, or the implementor of the file-system? It
seems to me that the end-user doesn't care, and just wants the file-system to
work as expected. I don't think we're really talking about the end-user.
No, this is exactly about end-user expectations. Imagine a complicated
heavy-loaded shared storage where handling FUSE_RELEASE in userspace may
take a few minutes. In close_wait=0 case, an end-user who has just
called close(2) has no idea when it's safe to access the file from
another node or even when it's OK to umount filesystem.
The implementor of a file-system, on the other hand, might want the semantics
for close_wait on some files, but not on others. Won't there be a performance
impact? Some distributed file-systems might want this on specific files only.
Implementing it as a flag on the struct fuse_file_info gives the flexibility to
the file-system implementor.
fuse_file_info is an userspace structure, in-kernel fuse knows nothing
about it. In close_wait=1 case, nothing prevents a file-system
implementation from ACK-ing FUSE_RELEASE request immediately (for
specific files) and schedule actual handling for future processing.
Thanks,
Maxim
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