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// Copyright (C) 2020-2022 Alibaba Cloud. All rights reserved.
// SPDX-License-Identifier: Apache-2.0
use std::str::FromStr;
use std::time::Duration;
/// The caching policy that the file system should report to the FUSE client. By default the FUSE
/// protocol uses close-to-open consistency. This means that any cached contents of the file are
/// invalidated the next time that file is opened.
#[derive(Debug, Default, Clone, Eq, PartialEq)]
pub enum CachePolicy {
/// The client should never cache file data and all I/O should be directly forwarded to the
/// server. This policy must be selected when file contents may change without the knowledge of
/// the FUSE client (i.e., the file system does not have exclusive access to the directory).
Never,
/// This is almost same as Never, but it allows page cache of directories, dentries and attr
/// cache in guest. In other words, it acts like cache=never for normal files, and like
/// cache=always for directories, besides, metadata like dentries and attrs are kept as well.
/// This policy can be used if:
/// 1. the client wants to use Never policy but it's performance in I/O is not good enough
/// 2. the file system has exclusive access to the directory
/// 3. cache directory content and other fs metadata can make a difference on performance.
Metadata,
/// The client is free to choose when and how to cache file data. This is the default policy and
/// uses close-to-open consistency as described in the enum documentation.
#[default]
Auto,
/// The client should always cache file data. This means that the FUSE client will not
/// invalidate any cached data that was returned by the file system the last time the file was
/// opened. This policy should only be selected when the file system has exclusive access to the
/// directory.
Always,
}
impl FromStr for CachePolicy {
type Err = &'static str;
fn from_str(s: &str) -> Result<Self, Self::Err> {
match s {
"never" | "Never" | "NEVER" | "none" | "None" | "NONE" => Ok(CachePolicy::Never),
"metadata" => Ok(CachePolicy::Metadata),
"auto" | "Auto" | "AUTO" => Ok(CachePolicy::Auto),
"always" | "Always" | "ALWAYS" => Ok(CachePolicy::Always),
_ => Err("invalid cache policy"),
}
}
}
/// Options that configure the behavior of the passthrough fuse file system.
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct Config {
/// How long the FUSE client should consider file and directory attributes to be valid. If the
/// attributes of a file or directory can only be modified by the FUSE client (i.e., the file
/// system has exclusive access), then this should be set to a large value.
///
/// The default value for this option is 5 seconds.
pub attr_timeout: Duration,
/// How long the FUSE client should consider directory entries to be valid. If the contents of a
/// directory can only be modified by the FUSE client (i.e., the file system has exclusive
/// access), then this should be a large value.
///
/// The default value for this option is 5 seconds.
pub entry_timeout: Duration,
/// Same as `attr_timeout`, override `attr_timeout` config, but only take effect on directories
/// when specified. This is useful to set different timeouts for directories and regular files.
pub dir_attr_timeout: Option<Duration>,
/// Same as `entry_timeout`, override `entry_timeout` config, but only take effect on
/// directories when specified. This is useful to set different timeouts for directories and
/// regular files.
pub dir_entry_timeout: Option<Duration>,
/// The caching policy the file system should use. See the documentation of `CachePolicy` for
/// more details.
pub cache_policy: CachePolicy,
/// Whether the file system should enable writeback caching. This can improve performance as it
/// allows the FUSE client to cache and coalesce multiple writes before sending them to the file
/// system. However, enabling this option can increase the risk of data corruption if the file
/// contents can change without the knowledge of the FUSE client (i.e., the server does **NOT**
/// have exclusive access). Additionally, the file system should have read access to all files
/// in the directory it is serving as the FUSE client may send read requests even for files
/// opened with `O_WRONLY`.
///
/// Therefore callers should only enable this option when they can guarantee that: 1) the file
/// system has exclusive access to the directory and 2) the file system has read permissions for
/// all files in that directory.
///
/// The default value for this option is `false`.
pub writeback: bool,
/// The path of the root directory.
///
/// The default is `/`.
pub root_dir: String,
/// Whether the file system should support Extended Attributes (xattr). Enabling this feature may
/// have a significant impact on performance, especially on write parallelism. This is the result
/// of FUSE attempting to remove the special file privileges after each write request.
///
/// The default value for this options is `false`.
pub xattr: bool,
/// To be compatible with Vfs and PseudoFs, PassthroughFs needs to prepare
/// root inode before accepting INIT request.
///
/// The default value for this option is `true`.
pub do_import: bool,
/// Control whether no_open is allowed.
///
/// The default value for this option is `false`.
pub no_open: bool,
/// Control whether no_opendir is allowed.
///
/// The default value for this option is `false`.
pub no_opendir: bool,
/// Control whether kill_priv_v2 is enabled.
///
/// The default value for this option is `false`.
pub killpriv_v2: bool,
/// Whether to use file handles to reference inodes. We need to be able to open file
/// descriptors for arbitrary inodes, and by default that is done by storing an `O_PATH` FD in
/// `InodeData`. Not least because there is a maximum number of FDs a process can have open
/// users may find it preferable to store a file handle instead, which we can use to open an FD
/// when necessary.
/// So this switch allows to choose between the alternatives: When set to `false`, `InodeData`
/// will store `O_PATH` FDs. Otherwise, we will attempt to generate and store a file handle
/// instead.
///
/// The default is `false`.
pub inode_file_handles: bool,
/// Control whether readdir/readdirplus requests return zero dirent to client, as if the
/// directory is empty even if it has children.
pub no_readdir: bool,
/// Control whether to refuse operations which modify the size of the file. For a share memory
/// file mounted from host, seal_size can prohibit guest to increase the size of
/// share memory file to attack the host.
pub seal_size: bool,
/// Whether count mount ID or not when comparing two inodes. By default we think two inodes
/// are same if their inode number and st_dev are the same. When `enable_mntid` is set as
/// 'true', inode's mount ID will be taken into account as well. For example, bindmount the
/// same file into virtiofs' source dir, the two bindmounted files will be identified as two
/// different inodes when this option is true, so the don't share pagecache.
///
/// The default value for this option is `false`.
pub enable_mntid: bool,
/// What size file supports dax
/// * If dax_file_size == None, DAX will disable to all files.
/// * If dax_file_size == 0, DAX will enable all files.
/// * If dax_file_size == N, DAX will enable only when the file size is greater than or equal
/// to N Bytes.
pub dax_file_size: Option<u64>,
/// Reduce memory consumption by directly use host inode when possible.
///
/// When set to false, a virtual inode number will be allocated for each file managed by
/// the passthroughfs driver. A map is used to maintain the relationship between virtual
/// inode numbers and host file objects.
/// When set to true, the host inode number will be directly used as virtual inode number
/// if it's less than the threshold (1 << 47), so reduce memory consumed by the map.
/// A virtual inode number will still be allocated and maintained if the host inode number
/// is bigger than the threshold.
/// The default value for this option is `false`.
pub use_host_ino: bool,
/// Whether the file system should honor the O_DIRECT flag. If this option is disabled,
/// that flag will be filtered out at `open_inode`.
///
/// The default is `true`.
pub allow_direct_io: bool,
}
impl Default for Config {
fn default() -> Self {
Config {
entry_timeout: Duration::from_secs(5),
attr_timeout: Duration::from_secs(5),
cache_policy: Default::default(),
writeback: false,
root_dir: String::from("/"),
xattr: false,
do_import: true,
no_open: false,
no_opendir: false,
killpriv_v2: false,
inode_file_handles: false,
no_readdir: false,
seal_size: false,
enable_mntid: false,
dax_file_size: None,
dir_entry_timeout: None,
dir_attr_timeout: None,
use_host_ino: false,
allow_direct_io: true,
}
}
}