Copyright	(c) 2020 Composewell Technologies
License	BSD-3-Clause
Maintainer	streamly@composewell.com
Stability	experimental
Portability	GHC
Safe Haskell	None
Language	Haskell2010

Streamly.Internal.FileSystem.Event.Linux

Contents

Subscribing to events
Handling Events
Debugging

Description

Overview

Use watchPaths with a list of file system paths you want to watch as argument. It returns a stream of Event representing the file system events occurring under the watched paths.

Stream.mapM_ (putStrLn . showEvent) $ watchPaths [Array.fromCString# "dir"#]

Event is an opaque type. Accessor functions (e.g. showEvent above) provided in this module are used to determine the attributes of the event.

Identical successive events may be coalesced into a single event.

Design notes

For reference documentation see:

inotify man page

We try to keep the macOS/Linux/Windows event handling APIs and defaults semantically and syntactically as close as possible.

BUGs

When testing on Linux Kernel version 5.3.0-53-generic #47-Ubuntu, the last event for the root path seems to be delayed until one more event occurs.

Differences between macOS and Linux APIs:

macOS watch is based on the path provided to it, if the path is deleted and recreated it will still be watched, if the path moves to another path it won't be watched anymore. Whereas Linux watch is based on a handle to the path, if the path is deleted and recreated it won't be watched, if the path moves to another it can still be watched (though this is configurable).

macOS watches the directory hierarchy recursively, Linux watches only one level of dir, recursive watch has to be built in user space by watching for create events and adding the new directories to the watch. Not sure how this will scale for too many paths.
In macOS the path of the subject of the event is absolute, in Linux the path is the name of the object inside the dir being watched.
On Linux watchPaths fails if a path does not exist, on macOS it does not fail.

Synopsis

data Config = Config {
- watchRec :: Bool
- createFlags :: Word32
}
data Switch
- = On
- | Off
defaultConfig :: Config
setRecursiveMode :: Switch -> Config -> Config
setFollowSymLinks :: Switch -> Config -> Config
setUnwatchMoved :: Switch -> Config -> Config
setOneShot :: Switch -> Config -> Config
setOnlyDir :: Switch -> Config -> Config
data WhenExists
- = AddIfExists
- | ReplaceIfExists
setWhenExists :: WhenExists -> Config -> Config
setRootDeleted :: Switch -> Config -> Config
setRootMoved :: Switch -> Config -> Config
setRootPathEvents :: Switch -> Config -> Config
setAttrsModified :: Switch -> Config -> Config
setAccessed :: Switch -> Config -> Config
setOpened :: Switch -> Config -> Config
setWriteClosed :: Switch -> Config -> Config
setNonWriteClosed :: Switch -> Config -> Config
setCreated :: Switch -> Config -> Config
setDeleted :: Switch -> Config -> Config
setMovedFrom :: Switch -> Config -> Config
setMovedTo :: Switch -> Config -> Config
setModified :: Switch -> Config -> Config
setAllEvents :: Switch -> Config -> Config
watch :: NonEmpty (Array Word8) -> SerialT IO Event
watchRecursive :: NonEmpty (Array Word8) -> SerialT IO Event
watchWith :: (Config -> Config) -> NonEmpty (Array Word8) -> SerialT IO Event
addToWatch :: Config -> Watch -> Array Word8 -> Array Word8 -> IO ()
removeFromWatch :: Watch -> Array Word8 -> IO ()
data Event = Event {
- eventWd :: CInt
- eventFlags :: Word32
- eventCookie :: Word32
- eventRelPath :: Array Word8
- eventMap :: IntMap (Array Word8, Array Word8)
}
getRoot :: Event -> Array Word8
getRelPath :: Event -> Array Word8
getAbsPath :: Event -> Array Word8
getCookie :: Event -> Cookie
isRootPathEvent :: Event -> Bool
isRootUnwatched :: Event -> Bool
isRootDeleted :: Event -> Bool
isRootMoved :: Event -> Bool
isRootUnmounted :: Event -> Bool
isAttrsModified :: Event -> Bool
isAccessed :: Event -> Bool
isOpened :: Event -> Bool
isWriteClosed :: Event -> Bool
isNonWriteClosed :: Event -> Bool
isCreated :: Event -> Bool
isDeleted :: Event -> Bool
isMovedFrom :: Event -> Bool
isMovedTo :: Event -> Bool
isMoved :: Event -> Bool
isModified :: Event -> Bool
isDir :: Event -> Bool
isEventsLost :: Event -> Bool
showEvent :: Event -> String

Subscribing to events

Default configuration

data Config Source #

Watch configuration, used to specify the events of interest and the behavior of the watch.

Pre-release

Constructors

Config
Fields watchRec :: Bool createFlags :: Word32

data Switch Source #

Whether a setting is On or Off.

Pre-release

Constructors

On
Off

Instances

Instances details

Show Switch Source #
Instance details Defined in Streamly.Internal.FileSystem.Event.Linux Methods showsPrec :: Int -> Switch -> ShowS # show :: Switch -> String # showList :: [Switch] -> ShowS #
Eq Switch Source #
Instance details Defined in Streamly.Internal.FileSystem.Event.Linux Methods (==) :: Switch -> Switch -> Bool # (/=) :: Switch -> Switch -> Bool #

defaultConfig :: Config Source #

The default configuration settings are:

The tunable events enabled by default are:

setCreated On
setDeleted On
setMovedFrom On
setMovedTo On
setModified On

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Watch Behavior

setRecursiveMode :: Switch -> Config -> Config Source #

Watch the whole directory tree recursively instead of watching just one level of directory.

default: Off

Pre-release

setFollowSymLinks :: Switch -> Config -> Config Source #

If the pathname to be watched is a symbolic link then watch the target of the symbolic link instead of the symbolic link itself.

Note that the path location in the events is through the original symbolic link path rather than the resolved path.

default: On

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setUnwatchMoved :: Switch -> Config -> Config Source #

If an object moves out of the directory being watched then stop watching it.

default: On

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setOneShot :: Switch -> Config -> Config Source #

Watch the object only for one event and then remove it from the watch.

default: Off

Pre-release

setOnlyDir :: Switch -> Config -> Config Source #

Watch the object only if it is a directory. This provides a race-free way to ensure that the watched object is a directory.

default: Off

Pre-release

data WhenExists Source #

What to do if a watch already exists when openWatch or addToWatch is called for a path.

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Constructors

AddIfExists	Do not set an existing setting to `Off` only set to `On`
ReplaceIfExists	Replace the existing settings with new settings

setWhenExists :: WhenExists -> Config -> Config Source #

When adding a new path to the watch, specify what to do if a watch already exists on that path.

default: FailIfExists

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Events of Interest

Root Path Events

setRootDeleted :: Switch -> Config -> Config Source #

Report when the watched path itself gets deleted.

default: On

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setRootMoved :: Switch -> Config -> Config Source #

Report when the watched root path itself gets renamed.

default: On

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setRootPathEvents :: Switch -> Config -> Config Source #

Report when the watched root path itself gets deleted or renamed.

default: On

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Item Level Metadata change

setAttrsModified :: Switch -> Config -> Config Source #

Report when the metadata e.g. owner, permission modes, modifications times of an object changes.

default: On

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Item Level Access

setAccessed :: Switch -> Config -> Config Source #

Report when a file is accessed.

default: On

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setOpened :: Switch -> Config -> Config Source #

Report when a file is opened.

default: On

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setWriteClosed :: Switch -> Config -> Config Source #

Report when a file that was opened for writes is closed.

default: On

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setNonWriteClosed :: Switch -> Config -> Config Source #

Report when a file that was opened for not writing is closed.

default: On

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Item CRUD events

setCreated :: Switch -> Config -> Config Source #

Report when a file is created.

default: On

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setDeleted :: Switch -> Config -> Config Source #

Report when a file is deleted.

default: On

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setMovedFrom :: Switch -> Config -> Config Source #

Report the source of a move.

default: On

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setMovedTo :: Switch -> Config -> Config Source #

Report the target of a move.

default: On

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setModified :: Switch -> Config -> Config Source #

Report when a file is modified.

default: On

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setAllEvents :: Switch -> Config -> Config Source #

Set all tunable events On or Off. Equivalent to setting:

setRootDeleted
setRootMoved
setAttrsModified
setAccessed
setOpened
setWriteClosed
setNonWriteClosed
setCreated
setDeleted
setMovedFrom
setMovedTo
setModified

Pre-release

Watch APIs

watch :: NonEmpty (Array Word8) -> SerialT IO Event Source #

Same as watchWith using defaultConfig and non-recursive mode.

>>> watch = watchWith id

Pre-release

watchRecursive :: NonEmpty (Array Word8) -> SerialT IO Event Source #

Same as watchWith using defaultConfig and recursive mode.

>>> watchRecursive = watchWith (setRecursiveMode On)

See watchWith for pitfalls and bugs when using recursive watch on Linux.

Pre-release

watchWith :: (Config -> Config) -> NonEmpty (Array Word8) -> SerialT IO Event Source #

Start monitoring a list of file system paths for file system events with the supplied configuration operation over the defaultConfig. The paths could be files or directories. When recursive mode is set and the path is a directory, the whole directory tree under it is watched recursively. Monitoring starts from the current time onwards. The paths are specified as UTF-8 encoded Array of Word8.

Non-existing Paths: the API fails if a watch is started on a non-exsting path.

Performance: Note that recursive watch on a large directory tree could be expensive. When starting a watch, the whole tree must be read and watches are started on each directory in the tree. The initial time to start the watch as well as the memory required is proportional to the number of directories in the tree.

Bugs: When new directories are created under the tree they are added to the watch on receiving the directory create event. However, the creation of a dir and adding a watch for it is not atomic. The implementation takes care of this and makes sure that watches are added for all directories. However, In the mean time, the directory may have received more events which may get lost. Handling of any such lost events is yet to be implemented.

See the Linux inotify man page for more details.

watchwith
     (setFollowSymLinks On . setUnwatchMoved Off)
     [Array.fromCString# "dir"#]

Pre-release

addToWatch :: Config -> Watch -> Array Word8 -> Array Word8 -> IO () Source #

addToWatch cfg watch root subpath adds subpath to the list of paths being monitored under root via the watch handle watch. root must be an absolute path and subpath must be relative to root.

Pre-release

removeFromWatch :: Watch -> Array Word8 -> IO () Source #

Remove an absolute root path from a Watch, if a path was moved after adding you need to provide the original path which was used to add the Watch.

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Handling Events

data Event Source #

An Event generated by the file system. Use the accessor functions to examine the event.

Pre-release

Constructors

Event
Fields eventWd :: CInt eventFlags :: Word32 eventCookie :: Word32 eventRelPath :: Array Word8 eventMap :: IntMap (Array Word8, Array Word8)

Instances

Instances details

Show Event Source #
Instance details Defined in Streamly.Internal.FileSystem.Event.Linux Methods showsPrec :: Int -> Event -> ShowS # show :: Event -> String # showList :: [Event] -> ShowS #
Eq Event Source #
Instance details Defined in Streamly.Internal.FileSystem.Event.Linux Methods (==) :: Event -> Event -> Bool # (/=) :: Event -> Event -> Bool #
Ord Event Source #
Instance details Defined in Streamly.Internal.FileSystem.Event.Linux Methods compare :: Event -> Event -> Ordering # (<) :: Event -> Event -> Bool # (<=) :: Event -> Event -> Bool # (>) :: Event -> Event -> Bool # (>=) :: Event -> Event -> Bool # max :: Event -> Event -> Event # min :: Event -> Event -> Event #

getRoot :: Event -> Array Word8 Source #

Get the watch root corresponding to the Event.

Note that if a path was moved after adding to the watch, this will give the original path and not the new path after moving.

TBD: we can possibly update the watch root on a move self event.

Pre-release

getRelPath :: Event -> Array Word8 Source #

Get the file system object path for which the event is generated, relative to the watched root. The path is a "/" separated array of bytes.

Pre-release

getAbsPath :: Event -> Array Word8 Source #

Get the absolute file system object path for which the event is generated.

When the watch root is a symlink, the absolute path returned is via the original symlink and not through the resolved path.

Pre-release

getCookie :: Event -> Cookie Source #

Cookie is set when a rename occurs. The cookie value can be used to connect the isMovedFrom and isMovedTo events, if both the events belong to the same move operation then they will have the same cookie value.

Pre-release

Root Level Events

isRootPathEvent :: Event -> Bool Source #

Determine whether the event indicates a change of path of the monitored object itself. Note that the object may become unreachable or deleted after a change of path.

Occurs only for a watched path

Pre-release

isRootUnwatched :: Event -> Bool Source #

A path was removed from the watch explicitly using removeFromWatch or automatically (file was deleted, or filesystem was unmounted).

Note that in recursive watch mode all the subdirectories are watch roots, therefore, they will all generate this event.

Occurs only for a watched path

Pre-release

isRootDeleted :: Event -> Bool Source #

Watched file/directory was itself deleted. (This event also occurs if an object is moved to another filesystem, since mv(1) in effect copies the file to the other filesystem and then deletes it from the original filesystem.) In addition, an isRootUnwatched event will subsequently be generated for the watch descriptor.

Note that in recursive watch mode all the subdirectories are watch roots, therefore, they will all generate this event.

Occurs only for a watched path

Pre-release

isRootMoved :: Event -> Bool Source #

Watched file/directory was itself moved within the file system.

Note that in recursive watch mode all the subdirectories are watch roots, therefore, they will all generate this event.

Occurs only for a watched path

Pre-release

isRootUnmounted :: Event -> Bool Source #

Filesystem containing watched object was unmounted. In addition, an isRootUnwatched event will subsequently be generated for the watch descriptor.

Occurs only for a watched path

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Item Level Metadata change

isAttrsModified :: Event -> Bool Source #

Determine whether the event indicates inode metadata change for an object contained within the monitored path.

Metadata change may include, permissions (e.g., chmod(2)), timestamps (e.g., utimensat(2)), extended attributes (setxattr(2)), link count (since Linux 2.6.25; e.g., for the target of link(2) and for unlink(2)), and user/group ID (e.g., chown(2)).

Can occur for watched path or a file inside it

Pre-release

Item Level Access

isAccessed :: Event -> Bool Source #

File was accessed (e.g. read, execve).

Occurs only for a file inside the watched directory

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isOpened :: Event -> Bool Source #

File or directory was opened.

Occurs only for a file inside the watched directory

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isWriteClosed :: Event -> Bool Source #

File opened for writing was closed.

Occurs only for a file inside the watched directory

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isNonWriteClosed :: Event -> Bool Source #

File or directory opened for read but not write was closed.

Can occur for watched path or a file inside it

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Item Level CRUD events

isCreated :: Event -> Bool Source #

File/directory created in watched directory (e.g., open(2) O_CREAT, mkdir(2), link(2), symlink(2), bind(2) on a UNIX domain socket).