On Sep 21 2017, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> Thanks for your feedback. Fixed and expanded version:
>
> Fuse supports the following I/O modes:
>
> - direct-io
> - cached
> + write-through
> + writeback-cache
>
> The direct-io mode can be selected with the FOPEN_DIRECT_IO flag in the
> FUSE_OPEN reply.
>
> In direct-io mode the page cache is completely bypassed for reads and writes.
> No read-ahead takes place. Shared mmap is disabled.
>
> In cached mode reads may be satisfied from the page cache, and data may be
> read-ahead by the kernel to fill the cache. The cache is always kept consistent
> after any writes to the file. All mmap modes are supported.
>
> The cached mode has two sub modes controlling how writes are handled. The
> write-through mode is the default and is supported on all kernels. The
> writeback-cache mode may be selected by the FUSE_WRITEBACK_CACHE flag in the
> FUSE_INIT reply.
>
> In write-through mode each write is immediately sent to userspace as one or more
> WRITE requests, as well as updating any cached pages (and caching previously
> uncached, but fully written pages). No READ requests are ever sent for writes,
> so when an uncached page is partially written, the page is discarded.
>
> In writeback-cache mode (enabled by the FUSE_WRITEBACK_CACHE flag) writes go to
> the cache only, which means that the write(2) syscall can often complete very
> fast. Dirty pages are written back implicitly (background writeback or page
> reclaim on memory pressure) or explicitly (invoked by fsync(2)).
I think it would be useful to mention if the cache is flushed when the
file is not opened anymore, or (if not) to explicitly say that that's
not the case.
> This mode assumes that the file is never changed outside the mounted
> filesystem
This sounds a little awkward. How about "assumes that all changes to the
filesystem go through the FUSE kernel module"
> (the size time attributes are kept uptodate by the kernel),
"size and atime/ctime/mtime attributes", and I think "uptodate" should
be up-to-date.
> so it's not suitable for any any network filesystem
duplicated "any"
I think this is great. I may work on similar documentation for some of
the other stuff that currently lives only in include/fuse*.h
Best,
-Nikolaus
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