linux.git/fs/fuse/dir.c, branch v2.6.26

fuse: update file size on short read

2008-04-30T15:29:50+00:00

If the READ request returned a short count, then either

  - cached size is incorrect
  - filesystem is buggy, as short reads are only allowed on EOF

So assume that the size is wrong and refresh it, so that cached read() doesn't
zero fill the missing chunk.

Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: support writable mmap

2008-04-30T15:29:50+00:00

Quoting Linus (3 years ago, FUSE inclusion discussions):

  "User-space filesystems are hard to get right. I'd claim that they
   are almost impossible, unless you limit them somehow (shared
   writable mappings are the nastiest part - if you don't have those,
   you can reasonably limit your problems by limiting the number of
   dirty pages you accept through normal "write()" calls)."

Instead of attempting the impossible, I've just waited for the dirty page
accounting infrastructure to materialize (thanks to Peter Zijlstra and
others).  This nicely solved the biggest problem: limiting the number of pages
used for write caching.

Some small details remained, however, which this largish patch attempts to
address.  It provides a page writeback implementation for fuse, which is
completely safe against VM related deadlocks.  Performance may not be very
good for certain usage patterns, but generally it should be acceptable.

It has been tested extensively with fsx-linux and bash-shared-mapping.

Fuse page writeback design
--------------------------

fuse_writepage() allocates a new temporary page with GFP_NOFS|__GFP_HIGHMEM.
It copies the contents of the original page, and queues a WRITE request to the
userspace filesystem using this temp page.

The writeback is finished instantly from the MM's point of view: the page is
removed from the radix trees, and the PageDirty and PageWriteback flags are
cleared.

For the duration of the actual write, the NR_WRITEBACK_TEMP counter is
incremented.  The per-bdi writeback count is not decremented until the actual
write completes.

On dirtying the page, fuse waits for a previous write to finish before
proceeding.  This makes sure, there can only be one temporary page used at a
time for one cached page.

This approach is wasteful in both memory and CPU bandwidth, so why is this
complication needed?

The basic problem is that there can be no guarantee about the time in which
the userspace filesystem will complete a write.  It may be buggy or even
malicious, and fail to complete WRITE requests.  We don't want unrelated parts
of the system to grind to a halt in such cases.

Also a filesystem may need additional resources (particularly memory) to
complete a WRITE request.  There's a great danger of a deadlock if that
allocation may wait for the writepage to finish.

Currently there are several cases where the kernel can block on page
writeback:

  - allocation order is larger than PAGE_ALLOC_COSTLY_ORDER
  - page migration
  - throttle_vm_writeout (through NR_WRITEBACK)
  - sync(2)

Of course in some cases (fsync, msync) we explicitly want to allow blocking.
So for these cases new code has to be added to fuse, since the VM is not
tracking writeback pages for us any more.

As an extra safetly measure, the maximum dirty ratio allocated to a single
fuse filesystem is set to 1% by default.  This way one (or several) buggy or
malicious fuse filesystems cannot slow down the rest of the system by hogging
dirty memory.

With appropriate privileges, this limit can be raised through
'/sys/class/bdi//max_ratio'.

Signed-off-by: Miklos Szeredi 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: fix permission checking

2008-02-24T01:12:13+00:00

I added a nasty local variable shadowing bug to fuse in 2.6.24, with the
result, that the 'default_permissions' mount option is basically ignored.

How did this happen?

 - old err declaration in inner scope
 - new err getting declared in outer scope
 - 'return err' from inner scope getting removed
 - old declaration not being noticed

-Wshadow would have saved us, but it doesn't seem practical for
the kernel :(

More testing would have also saved us :((

Signed-off-by: Miklos Szeredi 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Convert ERR_PTR(PTR_ERR(p)) instances to ERR_CAST(p)

2008-02-07T16:42:26+00:00

Convert instances of ERR_PTR(PTR_ERR(p)) to ERR_CAST(p) using:

perl -spi -e 's/ERR_PTR[(]PTR_ERR[(](.*)[)][)]/ERR_CAST(\1)/' `grep -rl 'ERR_PTR[(]*PTR_ERR' fs crypto net security`

Signed-off-by: David Howells 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: fix attribute caching after create

2008-02-06T18:41:13+00:00

Invalidate attributes on create, since st_ctime is updated.  Reported by
Szabolcs Szakacsits.

Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: fix attribute caching after rename

2007-11-29T17:24:54+00:00

Invalidate attributes on rename, since some filesystems may update
st_ctime.  Reported by Szabolcs Szakacsits

Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: pass open flags to read and write

2007-11-29T17:24:54+00:00

Some open flags (O_APPEND, O_DIRECT) can be changed with fcntl(F_SETFL, ...)
after open, but fuse currently only sends the flags to userspace in open.

To make it possible to correcly handle changing flags, send the
current value to userspace in each read and write.

Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: cleanup: add fuse_get_attr_version()

2007-11-29T17:24:54+00:00

Extract repeated code into helper function, as suggested by Akpm.

Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: fix reading past EOF

2007-11-29T17:24:54+00:00

Currently reading a fuse file will stop at cached i_size and return
EOF, even though the file might have grown since the attributes were
last updated.

So detect if trying to read past EOF, and refresh the attributes
before continuing with the read.

Thanks to mpb for the report.

Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fuse: add blksize field to fuse_attr

2007-10-18T21:37:31+00:00

There are cases when the filesystem will be passed the buffer from a single
read or write call, namely:

 1) in 'direct-io' mode (not O_DIRECT), read/write requests don't go
    through the page cache, but go directly to the userspace fs

 2) currently buffered writes are done with single page requests, but
    if Nick's ->perform_write() patch goes it, it will be possible to
    do larger write requests.  But only if the original write() was
    also bigger than a page.

In these cases the filesystem might want to give a hint to the app
about the optimal I/O size.

Allow the userspace filesystem to supply a blksize value to be returned by
stat() and friends.  If the field is zero, it defaults to the old
PAGE_CACHE_SIZE value.

Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds