Commit Graph

274 Commits

Author SHA1 Message Date
Nick Craig-Wood
421585dd72 accounting: add context to Account and propagate changes #3257
This is preparation for getting the Accounting to check the context,
buf first we need to get it in place. Since this is one of those
changes that makes lots of noise, this is in a seperate commit.
2020-07-28 16:41:17 +01:00
Nick Craig-Wood
0272a7f405 mount: change interface of mount commands to take mount options
This is in preparation of being able to pass mount options to the rc
command "mount/mount"
2020-07-24 10:48:51 +01:00
Nick Craig-Wood
2871268505 mount: change interface of mount commands to take VFS
This is in preparation of being able to pass options to the rc command
"mount/mount"
2020-07-23 12:30:41 +01:00
Nick Craig-Wood
ddfde68140 vfs: fix directory locking caused by slow directory listings
Before this fix we took the directory lock to read the ModTime of the
directory. This was causing locking on directories which were being
re-read from the backend.

This commit gives the modtime its own lock so it can be read even when
the directory is being updated.

See: https://forum.rclone.org/t/high-cpu-load-with-rclone-mount/17604
2020-07-18 09:08:18 +01:00
Nick Craig-Wood
126efaadcc vfs: fix renamed files not being uploaded with --vfs-cache-mode minimal
Before this change files that were in the cache and renamed with
--vfs-cache-mode minimal weren't renamed at all.

This fixes the problem and adds tests for all the different
combinations of cache modes and in and out of the cache.
2020-07-15 16:22:12 +01:00
Nick Craig-Wood
2adc057d95 vfs: fix very high load caused by slow directory listings
In this commit (released in v1.52.0)

6ca7198f mount: fix disappearing cwd problem

SetSys was introduced to cache node lookups.

Unfortunately taking the vfs.(*Dir) lock in SetSys causes any FUSE
operations on a directory to pile up behind slow directory listings.

In some situations this leads to very high load.

This commit fixes it by using atomic operations to read and write the
Sys value make it independent of the lock.

See: https://forum.rclone.org/t/high-cpu-load-with-rclone-mount/17604
See: #4104
2020-07-15 16:22:12 +01:00
Nick Craig-Wood
b2f4f52b64 vfs cache: make logging consistent and remove some debug logging 2020-07-06 17:32:53 +01:00
Nick Craig-Wood
c65ed26a7e vfs: vfscache: Fix renaming of items while they are being uploaded
Previous to the fix, if an item was being uploaded and it was renamed,
the upload would fail with missing checksum errors.

This change cancels any uploads in progress if the file is renamed.
2020-07-06 17:32:53 +01:00
Nick Craig-Wood
df5dbaf49b vfs: writeback: add Rename call for renaming items in the writeback queue 2020-07-06 17:32:53 +01:00
Nick Craig-Wood
63ebe4ca8d vfs: Reduce logging of metadata expiry to debug 2020-07-02 14:52:12 +01:00
Nick Craig-Wood
96c2fdb445 vfs: update VFS help 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
8301a72453 vfs: Fix over downloading with --vfs-cache-mode full and --buffer-size 0
This was caused by the signal to stop buffering being ignored when
there was no buffer!

This is fixed by explicitly checking for no buffering and stopping.
2020-06-30 12:03:39 +01:00
Nick Craig-Wood
15402e46c9 vfs: Add recovered items on cache reload to directory listings
Before this change, if we restarted an upload after a restart then the
file would get uploaded but never added to the directory listings.

This change makes sure we add virtual items to the directory cache
when reloading the cache so that they show up properly.
2020-06-30 12:03:39 +01:00
Nick Craig-Wood
939860eb85 vfs: vfscache make TestCacheCleaner test more reliable 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
530dc77cde vfs: Fix race condition in vfscache 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
5db15cb157 vfs: make dir.ForgetAll and friends not forget virtual entries
Before this change dir.ForgetAll and vfs/forget would forget about
virtual directory entries.

This change preserves them.
2020-06-30 12:03:39 +01:00
Nick Craig-Wood
06a12f5e27 vfs: stop virtual directory entries dropping out of the directory cache
Rclone adds virtual directory entries to the directory cache when it
creates a file or directory.

Before this change these dropped out of the directory cache when the
directory cache was reloaded. This meant that when the directory cache
expired:

- On bucket based backends, empty directories would disappear
- When using VFS writeback, files in the process of uploading would disappear

This is fixed by keeping track of the virtual entries in each
directory. The virtual entries are removed when they become real - ie
the object is read back from the listing.

This also keeps tracks of deletes in the same way so if a file is
deleted, it will not re-appear when the directory cache is reloaded if
the deletion hasn't finished yet.
2020-06-30 12:03:39 +01:00
Nick Craig-Wood
143abe39f2 vfs: add tests for downloaders 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
ee04732cbb vfs: factor writeback and downloaders into their own packages 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
79455cc71e vfs: downloaders: remove unused osPath 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
042e5fe097 vfs: downloader: limit the reader to 10 errors before giving up 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
d273a9d82d vfs: remove items from writeback when dirty, don't just cancel the upload
This stops open items continually trying to be uploaded
2020-06-30 12:03:39 +01:00
Nick Craig-Wood
3eded3c4ac vfs: remove workaround Sleep() calls from tests 2020-06-30 12:03:39 +01:00
Nick Craig-Wood
ed32a759ed vfs: add test for writeBack.cancelUpload 2020-06-30 12:01:36 +01:00
Nick Craig-Wood
ef2d036884 vfs: make writeback heap sort in insertion order if expiry times equal
This makes the tests 100% consistent on platforms which have a lower
resolution timer like Windows.
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
746c41f527 vfs: fix race in writeback tests 2020-06-30 12:01:36 +01:00
Nick Craig-Wood
b0fb457746 vfs: add tests for writeback 2020-06-30 12:01:36 +01:00
Nick Craig-Wood
b9ff495483 vfs: writeback - stop the timer explicitly on transfers exceeded 2020-06-30 12:01:36 +01:00
Nick Craig-Wood
8506066926 vfs: use call after functions in writeback to simplify code
This also fixes a bug in the uploader which didn't restart the timer
when the queue was empty.
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
43018973ac vfs: decouple writeback from Item so it can be tested 2020-06-30 12:01:36 +01:00
Nick Craig-Wood
7e4ba54608 vfs: allow ReadAt and WriteAt to run concurrently with themselves
This should help with throughput on mounts and help when multiple
readers have the file open.

See: https://forum.rclone.org/t/concurrent-read-accesses-on-the-same-file-through-rclone-vfs-mount/17192
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
2f66355f20 vfs: re-use existing VFS if possible 2020-06-30 12:01:36 +01:00
Nick Craig-Wood
7781ea8d59 vfs: add an optional fs parameter to vfs rc methods
Before this change we initialized the rc for a single VFS. However
rclone can have multiple VFSes in use now so this is no longer
adequate.

This change adds an optional fs parameter to all the VFS methods to
disambiguate VFSes when there is more than one in use.

It also adds a method vfs/list to show all the active VFSes.

This adds outline tests for the rc commands which didn't have tests
before.
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
fa472a340e vfs: fix writeback deadlocks and other bugs
- fix deadlock when cancelling upload
- fix double upload and panic after cancelled upload
- fix cancelation strategy of uploading files
    - don't cancel uploads if we don't modify the file
    - cancel uploads if we do modify the file
- fix deadlock between Item and writeback
- fix confusion about whether writeback item was being uploaded
- fix cornercases in cancelling uploads and removing files
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
279a516c53 vfs: add tests and fix bugs for vfscache.Item
Item
- Remove unused method getName
- Fix Truncate on unopened file
- Fix bug when downloading segments to fill out file on close
- Fix bug when WriteAt extends the file and we don't mark space as used

downloader
- Retry failed waiters every 5 seconds
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
9ac5c6de14 vfs: cache: rework file downloader
- Download to multiple places at once in the stream
- Restart as necessary
- Timeout unused downloaders
- Close reader if too much data skipped
- Only use one file handle as use item for writing
- Implement --vfs-read-chunk-size and --vfs-read-chunk-limit
- fix deadlock between asyncbuffer and vfs cache downloader
- fix display of stream abandoned error which should be ignored
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
58a7faa281 vfs: Make tests run reliably
On file Remove
- cancel any writebacks in progress
- ignore error message deleting non existent file if file was in the
  process of being uploaded

Writeback
- Don't transfer the file if it has disappeared in the meantime
- Take our own copy of the file name to avoid deadlocks
- Fix delayed retry logic
- Wait for upload to finish when cancelling upload

Fix race condition in item saving

Fix race condition in vfscache test

Make sure we delete the file on the error path - this makes cascading
failures much less likely
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
496a87a665 vfs: restart pending uploads on restart of the cache 2020-06-30 12:01:36 +01:00
Nick Craig-Wood
e4e53a2e61 vfs: add --vfs-writeback option to delay writes back to cloud storage
This is enabled by default and can be disabled with --vfs-writeback 0
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
28255f1bac vfs: fix errors when using > 260 char files in the cache in Windows
This makes the cache use UNC paths on Windows. This stops the cache
exploding when using > 260 character paths
2020-06-30 12:01:36 +01:00
Nick Craig-Wood
917cb4acb3 vfs: implement partial reads in --vfs-cache-mode full
This allows reads to only read part of the file and it keeps on disk a
cache of what parts of each file have been loaded.

File data itself is kept in sparse files.
2020-06-30 12:01:36 +01:00
Rob Calistri
b2ded6212b vfs: Change modtime of file before upload to current
Previously files before they get uploaded will inherit the directory modtime.  This changes that to use the current time instead.
2020-06-10 12:10:50 +01:00
Nick Craig-Wood
88df5927f9 vfs: funnel all read/write calls through ReadAt/WriteAt
This is in preparation for partial reads for read/write files
2020-06-09 18:07:41 +01:00
Nick Craig-Wood
8c37262e05 vfs: don't use embedded methods for read/write handles for clarity 2020-06-09 18:07:23 +01:00
Nick Craig-Wood
05bc19c331 vfs: Remove uneeded locking from read write handle String() 2020-06-09 18:04:50 +01:00
Nick Craig-Wood
50e31c6636 vfs: fix OS vs Unix path confusion - fixes ChangeNotify on Windows
See: https://forum.rclone.org/t/windows-mount-polling-not-recognising-all-changes-made-by-another-box/16708
2020-06-03 17:05:58 +01:00
Nick Craig-Wood
1bd3365868 vfs: fix TestVFSStatfs with known total, used and unknown free 2020-05-25 16:46:56 +01:00
Martin Michlmayr
041b201abd doc: fix typos throughout docs and code 2020-05-25 11:23:58 +01:00
Martin Michlmayr
a36ef8582f doc: use consistent capitalization 2020-05-20 15:54:51 +01:00
Martin Michlmayr
4aee962233 doc: fix typos throughout docs and code 2020-05-20 15:54:51 +01:00
Nick Craig-Wood
951099dbed vfs: change default --vfs-read-wait to 20ms
In my testing with local and remote storage this is a good compromise
between delaying the seeks and failing to wait for in sequence reads.

See: https://forum.rclone.org/t/constantly-high-iowait-add-log/14156/40
2020-05-18 18:09:23 +01:00
Nick Craig-Wood
0f9267d5fc vfs: factor waiting code from read and writes into common function 2020-05-18 18:09:23 +01:00
Nick Craig-Wood
3de9bd9d04 vfs: fix hang in read wait code - Fixes #4039
Before this fix, rclone would sometimes hang in vfs.readAt().

This was due to a race condition causing rclone to miss the timeout
signal.

This was fixed by a small amount of extra locking.

This very likely also fixes a number of "failed to wait for
in-sequence read" errors.
2020-05-18 18:09:23 +01:00
Nick Craig-Wood
1a8c5708c5 vfs: ignore file not found errors from Hash in Read.Release
There is nothing we can do about this at this point and this error can
happen when moving files so we ignore it to clean the logs up.
2020-05-04 12:18:28 +01:00
Nick Craig-Wood
cfcdc85b26 vfs: Add SetSys() methods to Node to allow caching stuff on a node 2020-05-04 11:38:07 +01:00
Nick Craig-Wood
70db13e6e8 vfs: pin the Fs in use in the Fs cache
This means we can reliably look up the Fs from the cache when using
`backend/command`.
2020-05-01 17:11:45 +01:00
Nick Craig-Wood
77fb3c2511 vfs: bring DO NOT EDIT comments in line with "go help generate" 2020-04-30 12:24:44 +01:00
Nick Craig-Wood
86eaf43b00 vfs: fix tests for Statfs when running on backends with unknowns
This was broken in da41db4712
2020-04-22 18:14:03 +01:00
Nick Craig-Wood
eed9c5738d vfs: factor the vfs cache into its own package 2020-04-20 10:42:33 +01:00
Nick Craig-Wood
fd39cbc193 vfstests: move functional tests from mountlib and make them work with VFS
The tests are now run for the mount commands and for the plain VFS.

This makes the tests much easier to debug when running with a VFS than
through a mount.
2020-04-20 10:42:33 +01:00
Nick Craig-Wood
0961763082 vfs: add utility methods to match os package 2020-04-19 15:40:55 +01:00
Nick Craig-Wood
07908f3f54 vfs: bring open_tests.go generator back into line with the generated tests
In

54deb01f00 vfs: Make OpenFile and friends return EINVAL if O_RDONLY and O_TRUNC

The generated file open_test.go was edited directly without editing
the generator.

This commit brings the generator make_open_tests.go back into line
with that edit. It also makes it so `go generate` can be used to
regenerate the tests.
2020-04-19 15:18:49 +01:00
Nick Craig-Wood
1f50b70919 vfs: consistently use f.Path() or f._path() in File logs to avoid deadlocks
Previously we were using f which calls f.String() which calls f.Path()
which can cause a deadlock if uses carelessly.

This patch explicitly calls f.Path() or f._path() to bring attention
to the fact that there is a call to a method.
2020-04-19 15:16:43 +01:00
Nick Craig-Wood
19db0df639 vfs: stop reading Dir members from outside dir.go 2020-04-19 15:16:43 +01:00
Nick Craig-Wood
238f26cc90 vfs: stop reading File members from outside file.go
This also fixes locking for ReadFileHandle and WriteFileHandle
accessing File members
2020-04-19 15:16:43 +01:00
Nick Craig-Wood
268fcbb973 vfs: implement lock ordering between File and Dir to eliminate deadlocks
As part of this we take a copy of the directory path as calling
d.Path() violates the total locking order.

See the comment at the top of file.go for details
2020-04-19 15:16:43 +01:00
Nick Craig-Wood
da41db4712 vfs,mount,cmount: report 1PB free for unknown disk sizes
Factor the logic into the VFS layer so we don't have to duplicate it
into mount and cmount.

See: https://forum.rclone.org/t/rclone-mount-question/15454/
2020-04-11 13:31:10 +01:00
Nick Craig-Wood
3911a49256 vfs: make File lock and Dir lock not overlap to avoid deadlock
This was caused by this commit which wasn't part of 1.51.0

3c91abce74 vfs: fix race condition caused by unlocked reading of Dir.path
2020-04-02 21:14:45 +01:00
Yves G
b1b5e09081 vfs: make df output more consistent on a rclone mount.
When 2 values are known among vfs:{free,used,total}, compute the 3rd
2020-03-01 08:54:07 +00:00
Nick Craig-Wood
393b94bb70 vfs: add --vfs-read-wait and --vfs-write-wait flags
--vfs-read-wait duration    Time to wait for in-sequence read before seeking. (default 5ms)
    --vfs-write-wait duration   Time to wait for in-sequence write before giving error. (default 1s)

See: https://forum.rclone.org/t/constantly-high-iowait-add-log/14156
2020-02-27 16:12:33 +00:00
Nick Craig-Wood
3c91abce74 vfs: fix race condition caused by unlocked reading of Dir.path 2020-02-27 15:50:41 +00:00
Lars Lehtonen
4e1a511f88
vfs: explicitly ignore unused variables 2020-02-12 11:20:54 +00:00
Nick Craig-Wood
102a38bb95 docs: restore lost VFS poll interval docs
These came from 3d475dc0ee which unfortunately got added the
docs to the auto generated files.
2020-02-10 15:29:39 +00:00
Nick Craig-Wood
7a54e13110 docs: restore lost VFS case insensitive docs
These came from 1c4e33d4ad which unfortunately
added the docs to the auto generated files.
2020-02-10 15:29:39 +00:00
Nick Craig-Wood
84191ac6dc vfs: fix incorrect modtime for mv into mount with --vfs-cache-modes write
When a file has its modtime set while it is open we delay setting the
modtime until the file is closed.

The file is then uploaded in Flush. In Release we check the cached
file has been uploaded by comparing modtimes and or hashes and upload
it again if it has changed.

Before this change we forgot to change the time on the cached file
when we updated the time file on the object, so this mean that Release
reset the time to the wrong time and uploaded the file again on
remotes which don't support hashes (eg crypt).

The fix was to set the modtime of the cached file at the same time we
set the modtime of the remote object. This means that the files check
as identical in Release so it doesn't try to upload the file.

This means that we avoid a double upload and the modtime is correct.

See: https://forum.rclone.org/t/modification-time-with-vfs-cache/13906/8
2020-01-19 12:52:48 +00:00
Nick Craig-Wood
95c83b37fb vfs: only run TestRWCacheRename on remotes which can rename
This fixes the 1fichier integration tests.
2020-01-15 16:25:04 +00:00
Nick Craig-Wood
63128834da vfs: fix open file renaming on drive when using --vfs-cache-mode writes
Before this change, when uploading files from the VFS cache which were
pending a rename, rclone would use the new path of the object when
specifiying the destination remote.  This didn't cause a problem with
most backends as the subsequent rename did nothing, however with the
drive backend, since it updates objects, the incorrect Remote was
embedded in the object.  This caused the rename to apparently succeed
but the object be at the wrong location.

The fix for this was to make sure we upload to the path stored in the
object if available.

This problem was spotted by the new rename tests for the VFS layer.
2020-01-13 17:37:54 +00:00
Nick Craig-Wood
1b89b38a4c vfs: skip rename tests on remotes which can't rename 2020-01-05 12:34:47 +00:00
Nick Craig-Wood
1ab4985046 vfs: when renaming files in the cache, rename the cache item in memory too 2019-12-12 13:31:10 +00:00
Nick Craig-Wood
6e683b4359 vfs: fix rename of open files when using the VFS cache
Before this change, renaming an open file when using the VFS cache was
delayed until the file was closed.  This meant that the file was not
readable after a rename even though it is was in the cache.

After this change we rename the local cache file and the in memory
cache, delaying only the rename of the file in object storage.

See: https://forum.rclone.org/t/xen-orchestra-ebadf-bad-file-descriptor-write/13104
2019-12-12 13:31:10 +00:00
Nick Craig-Wood
241921c786 vfs: don't cache the path in RW file objects to fix renaming 2019-12-12 13:31:10 +00:00
Nick Craig-Wood
420ae905b5 vfs: make sure existing files opened for write show correct size
Before this change if an existing file was opened for write without
truncate its size would show as 0 rather than the full size of the
file.
2019-11-25 11:31:44 +00:00
Nick Craig-Wood
b5bb4c2a21 vfs: fix tests not to upload a 0 length file
Some remotes can't upload 0 length files, so this fixes the
TestCacheRename test so that it writes something to the file.
2019-11-15 09:26:40 +00:00
Nick Craig-Wood
358f5a8084 vfs: fix edge cases when reading ModTime from file
This fixes the unreliable test TestMount/CacheMode=full/TestFileModTime
2019-11-11 16:20:28 +00:00
Nick Craig-Wood
51efb349ac vfs: revise locking in file and dir to fix race conditions 2019-11-11 16:20:27 +00:00
Nick Craig-Wood
5beeac7959 vfs: make ReadAt for non cached files work better with non-sequential reads
This makes ReadAt for non cached files wait a short time (up to 5mS)
if it gets an out of order read (which would normally cause a seek and
which take a long time) to see if the gap will be filled with an in
order read.

This makes mount2 based on go-fuse work more efficiently and enables
async reading in normal mount.

A similar change was done for WriteAt in af030f74f5
2019-11-11 16:20:27 +00:00
Nick Craig-Wood
be5392f448 vfs: only calculate one hash for reads
This speeds up mounting on the local backend enormously.
2019-11-11 16:20:27 +00:00
Nick Craig-Wood
6150ae89d6 vfs: add a newly created file straight into the directory 2019-11-11 15:20:09 +00:00
Brett Dutro
53d55ae760 Add test for cache renaming functionality 2019-11-10 11:58:46 +00:00
Anagh Kumar Baranwal
5928704e1b On rename, rename in cache too if the file exists
Signed-off-by: Anagh Kumar Baranwal <6824881+darthShadow@users.noreply.github.com>
2019-11-10 11:58:46 +00:00
Brett Dutro
378a3f4133 mount: replace use of WriteAt with Write for cache mode >= writes and O_APPEND
os.File.WriteAt returns an error if a file was opened with O_APPEND.
This replaces it with os.File.Write if the file was opened with
O_APPEND.
2019-10-26 17:27:52 +01:00
Nick Craig-Wood
76f5e273d2 vfs: stop change notify polling clearing so much of the directory cache
Before this change, change notify polls would clear the directory
cache recursively. So uploading a file to the root would clear the
entire directory cache.

After this change we just invalidate the directory cache of the parent
directory of the item and if the item was a directory we invalidate it
too.
2019-10-21 20:51:11 +01:00
Nick Craig-Wood
1fe1a19339 vfs: stop empty dirs disappearing when renamed on bucket based remotes
Before this change when we renamed a directory this cleared the
directory cache for the parent directory too.

If the directory was remaining in the same parent this wasn't
necessary and caused the empty directory to fall out of the cache.

Fixes #3597
2019-10-14 14:38:30 +01:00
Brett Dutro
7d0d7e66ca vfs: move writeback of dirty data out of close() method into its own method (FlushWrites) and remove close() call from Flush()
If a file handle is duplicated with dup() and the duplicate handle is
flushed, rclone will go ahead and close the file, making the original
file handle stale. This change removes the close() call from Flush() and
replaces it with FlushWrites() so that the file only gets closed when
Release() is called. The new FlushWrites method takes care of actually
writing the file back to the underlying storage.

Fixes #3381
2019-10-09 10:07:29 +01:00
Nick Craig-Wood
ba121eddf0 vfs: make objects of unknown size readable through the VFS
These objects (eg Google Docs) appear with 0 length in the VFS.

Before this change, these only read 0 bytes.

After this change, even though the size appears to be 0, the objects
can be read to the end.  If the objects are read to the end then the
size on the handle will be updated.
2019-09-14 13:09:07 +01:00
Ivan Andreev
d0c6e5cf5a vfs: skip TestCaseSensitivity on case insensitive backends 2019-09-06 10:44:59 +01:00
Ivan Andreev
1c4e33d4ad vfs: add flag --vfs-case-insensitive for windows/macOS mounts
rclone mount when run on Windows & macOS will now default to `--vfs-case-insensitive`.
This means that
2019-09-04 21:30:48 +01:00
Nick Craig-Wood
077b45322d vfs: fix --vfs-cache-mode minimal,writes ignoring cached files
Before this change, with --vfs-cache-mode minimal,writes if files were
opened they would always be read from the remote, regardless of
whether they were in the cache or not.

This change checks to see if the file is in the cache when opening a
file with --vfs-cache-mode >= minimal and if so then it uses it from
the cache.

This makes --vfs-cache-mode writes in particular much more
efficient. No longer is a file uploaded (with write mode) then
immediately downloaded (with read only mode).

Fixes #3330
2019-08-23 13:58:15 +01:00
Nick Craig-Wood
d377842395 vfs: make write without cache more efficient
This updates the out of sequence write code to be more efficient using
a conditional lock with a timeout.
2019-08-08 12:37:50 +01:00
Nick Craig-Wood
e502be475a azureblob/b2/dropbox/gcs/koofr/qingstor/s3: fix 0 length files
In 0386d22cc9 we introduced a test for 0 length files read the
way mount does.

This test failed on these backends which we fix up here.
2019-08-06 15:18:08 +01:00