Add support for extended attributes to pipe fuse

[tcibinan]

Resolves #2847.

The pull request brings support for extended attributes processing. At the moment extended attributes are stored as cloud data storage object native tags. Currently AWS S3 is only supported on Linux/MacOS.

Filter extended attributes

As long as extended attribute calls are very common on Linux/MacOS then it is important to keep their processing efficient. Currently the processing efficiency is reached by filtering out all non user attributes. Notice that by default only attributes with user prefix are processed. All other attributes are ignored.

# the commands below work fine
setfattr -n user.key -v value ~/storage/mount/file.txt
getfattr -n user.key ~/storage/mount/file.txt
getfattr ~/storage/mount/file.txt

# the commands below fail because extended attribute name doesn't start with "user"
setfattr -n another.key -v value ~/storage/mount/file.txt
getfattr -n another.key ~/storage/mount/file.txt

Configure extended attribute filters

Additional custom mount options can be used to tweak extended attributes filters.

# extended attributes with "user" prefix are supported
pipe storage mount -c "xattrs-include-prefix=user" ...

# extended attributes with "user" or "admin" prefixes are supported
pipe storage mount -c "xattrs-include-prefix=user,xattrs-include-prefix=admin" ...

# all extended attributes are supported
pipe storage mount -c "xattrs-include-prefix=*" ...

# extended attributes without "user" prefix are supported
pipe storage mount -c "xattrs-exclude-prefix=user" ...

# extended attributes without "user" or "admin" prefixes are supported
pipe storage mount -c "xattrs-exclude-prefix=user,xattrs-exclude-prefix=admin" ...

# no extended attributes are supported
pipe storage mount -c "xattrs-exclude-prefix=*" ...

Disable file system operations

Support for certain file system operations disabling has been also introduced.

pipe storage mount -c "disabled-operation=listxattr,disabled-operation=setxattr,disabled-operation=removexattr" ...