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vfs: detect and recover from a file being removed externally from the cache 

Before this change if a file was removed from the cache while rclone
is running then rclone would not notice and proceed to re-create it
full of zeros.

This change notices files that we expect to have data in going missing
and if they do logs an ERROR recovers.

It isn't recommended deleting files from the cache manually with
rclone running!

See: https://forum.rclone.org/t/corrupted-data-streaming-after-vfs-meta-files-removed/18997
Fixes #4602
This commit is contained in:
Nick Craig-Wood 2020-09-11 16:34:54 +01:00
parent 313647bcf3
commit 18ccf0f871
1 changed files with 16 additions and 1 deletions
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17
vfs/vfscache/item.go
View File

@ -239,8 +239,23 @@ func (item *Item) _truncate(size int64) (err error) {
// Use open handle if available
fd := item.fd
if fd == nil {
// If the metadata says we have some blockes cached then the
// file should exist, so open without O_CREATE
oFlags := os.O_WRONLY
if item.info.Rs.Size() == 0 {
oFlags |= os.O_CREATE
}
osPath := item.c.toOSPath(item.name) // No locking in Cache
fd, err = file.OpenFile(osPath, os.O_CREATE|os.O_WRONLY, 0600)
fd, err = file.OpenFile(osPath, oFlags, 0600)
if err != nil && os.IsNotExist(err) {
// If the metadata has info but the file doesn't
// not exist then it has been externally removed
fs.Errorf(item.name, "vfs cache: detected external removal of cache file")
item.info.Rs = nil // show we have no blocks cached
item.info.Dirty = false // file can't be dirty if it doesn't exist
item._removeMeta("cache file externally deleted")
fd, err = file.OpenFile(osPath, os.O_CREATE|os.O_WRONLY, 0600)
}
if err != nil {
return errors.Wrap(err, "vfs cache: truncate: failed to open cache file")
}