Added information record support to fanotify

Author: carlvoller

src/sys/fanotify.rs

@@ -118,6 +118,46 @@ libc_bitflags! {
         FAN_REPORT_PIDFD;
         /// Make `FanotifyEvent::pid` return thread id. Since Linux 4.20.
         FAN_REPORT_TID;
+
+        /// Allows the receipt of events which contain additional information
+        /// about the underlying filesystem object correlated to an event.
+        ///
+        /// This will make `FanotifyEvent::fd` return `FAN_NOFD`.
+        /// This should be used with `Fanotify::read_events_with_info_records` to
+        /// recieve `FanotifyInfoRecord::Fid` info records.
+        /// Since Linux 5.1
+        FAN_REPORT_FID;
+
+        /// Allows the receipt of events which contain additional information
+        /// about the underlying filesystem object correlated to an event.
+        ///
+        /// This will make `FanotifyEvent::fd` return `FAN_NOFD`.
+        /// This should be used with `Fanotify::read_events_with_info_records` to
+        /// recieve `FanotifyInfoRecord::Fid` info records.
+        ///
+        /// An additional event of `FAN_EVENT_INFO_TYPE_DFID` will also be received,
+        /// encapsulating information about the target directory (or parent directory of a file)
+        /// Since Linux 5.9
+        FAN_REPORT_DIR_FID;
+
+        /// Events for fanotify groups initialized with this flag will contain additional
+        /// information about the child correlated with directory entry modification events.
+        /// This flag must be provided in conjunction with the flags `FAN_REPORT_FID`,
+        /// `FAN_REPORT_DIR_FID` and `FAN_REPORT_NAME`.
+        /// Since Linux 5.17
+        FAN_REPORT_TARGET_FID;
+
+        /// Events for fanotify groups initialized with this flag will contain additional
+        /// information about the name of the directory entry correlated to an event.  This
+        /// flag must be provided in conjunction with the flag `FAN_REPORT_DIR_FID`.
+        /// Since Linux 5.9
+        FAN_REPORT_NAME;
+
+        /// This is a synonym for `FAN_REPORT_DIR_FD | FAN_REPORT_NAME`.
+        FAN_REPORT_DFID_NAME;
+
+        /// This is a synonym for `FAN_REPORT_DIR_FD | FAN_REPORT_NAME | FAN_REPORT_TARGET_FID`.
+        FAN_REPORT_DFID_NAME_TARGET;
     }
 }
 
@@ -206,6 +246,33 @@ pub const FANOTIFY_METADATA_VERSION: u8 = libc::FANOTIFY_METADATA_VERSION;
 #[allow(missing_copy_implementations)]
 pub struct FanotifyEvent(libc::fanotify_event_metadata);
 
+/// After a [`libc::fanotify_event_metadata`], there can be 0 or more event_info
+/// structs depending on which InitFlags were used in [`Fanotify::init`].
+// Is not Clone due to pidfd in `libc::fanotify_event_info_pidfd`
+// Other fanotify_event_info records are not implemented as they don't exist in
+// the libc crate yet.
+#[derive(Debug, Eq, Hash, PartialEq)]
+#[allow(missing_copy_implementations)]
+pub enum FanotifyInfoRecord {
+    /// A [`libc::fanotify_event_info_fid`] event was recieved, usually as
+    /// a result of passing [`InitFlags::FAN_REPORT_FID`] or [`InitFlags::FAN_REPORT_DIR_FID`]
+    /// into [`Fanotify::init`]. The containing struct includes a `file_handle` for
+    /// use with `open_by_handle_at(2)`.
+    Fid(libc::fanotify_event_info_fid),
+
+    /// A [`libc::FAN_FS_ERROR`] event was received. This event occurs when
+    /// a filesystem event is detected. Only a single [`libc::FAN_FS_ERROR`] is
+    /// stored per filesystem at once, extra error messages are suppressed and
+    /// accounted for in the error_count field.
+    Error(libc::fanotify_event_info_error),
+
+    /// A [`libc::fanotify_event_info_pidfd`] event was recieved, usually as
+    /// a result of passing [`InitFlags::FAN_REPORT_PIDFD`] into [`Fanotify::init`].
+    /// The containing struct includes a `pidfd` for reliably determining
+    /// whether the process responsible for generating an event has been recycled or terminated
+    Pidfd(libc::fanotify_event_info_pidfd),
+}
+
 impl FanotifyEvent {
     /// Version number for the structure. It must be compared to
     /// `FANOTIFY_METADATA_VERSION` to verify compile version and runtime
@@ -341,6 +408,21 @@ impl Fanotify {
         Errno::result(res).map(|_| ())
     }
 
+    fn get_struct<T>(&self, buffer: &[u8; 4096], offset: usize) -> T {
+        let struct_size = size_of::<T>();
+        let struct_obj = unsafe {
+            let mut struct_obj = MaybeUninit::<T>::uninit();
+            std::ptr::copy_nonoverlapping(
+                buffer.as_ptr().add(offset),
+                struct_obj.as_mut_ptr().cast(),
+                (4096 - offset).min(struct_size),
+            );
+            struct_obj.assume_init()
+        };
+
+        struct_obj
+    }
+
     /// Read incoming events from the fanotify group.
     ///
     /// Returns a Result containing either a `Vec` of events on success or errno
@@ -382,6 +464,99 @@ impl Fanotify {
         Ok(events)
     }
 
+    /// Read incoming events and information records from the fanotify group.
+    ///
+    /// Returns a Result containing either a `Vec` of events and information records on success or errno
+    /// otherwise.
+    ///
+    /// # Errors
+    ///
+    /// Possible errors can be those that are explicitly listed in
+    /// [fanotify(2)](https://man7.org/linux/man-pages/man7/fanotify.2.html) in
+    /// addition to the possible errors caused by `read` call.
+    /// In particular, `EAGAIN` is returned when no event is available on a
+    /// group that has been initialized with the flag `InitFlags::FAN_NONBLOCK`,
+    /// thus making this method nonblocking.
+    pub fn read_events_with_info_records(
+        &self,
+    ) -> Result<Vec<(FanotifyEvent, Vec<FanotifyInfoRecord>)>> {
+        let metadata_size = size_of::<libc::fanotify_event_metadata>();
+        const BUFSIZ: usize = 4096;
+        let mut buffer = [0u8; BUFSIZ];
+        let mut events = Vec::new();
+        let mut offset = 0;
+
+        let nread = read(&self.fd, &mut buffer)?;
+
+        while (nread - offset) >= metadata_size {
+            let metadata = unsafe {
+                let mut metadata =
+                    MaybeUninit::<libc::fanotify_event_metadata>::uninit();
+                std::ptr::copy_nonoverlapping(
+                    buffer.as_ptr().add(offset),
+                    metadata.as_mut_ptr().cast(),
+                    (BUFSIZ - offset).min(metadata_size),
+                );
+                metadata.assume_init()
+            };
+
+            let mut remaining_len = metadata.event_len;
+            let mut info_records = Vec::new();
+            let mut current_event_offset = offset + metadata_size;
+
+            while remaining_len > 0 {
+                let header = self
+                    .get_struct::<libc::fanotify_event_info_header>(
+                        &buffer,
+                        current_event_offset,
+                    );
+
+                let info_record = match header.info_type {
+                    libc::FAN_EVENT_INFO_TYPE_FID => {
+                        let event_fid = self
+                            .get_struct::<libc::fanotify_event_info_fid>(
+                                &buffer,
+                                current_event_offset,
+                            );
+                        Some(FanotifyInfoRecord::Fid(event_fid))
+                    }
+                    libc::FAN_EVENT_INFO_TYPE_ERROR => {
+                        let error_fid = self
+                            .get_struct::<libc::fanotify_event_info_error>(
+                                &buffer,
+                                current_event_offset,
+                            );
+                        Some(FanotifyInfoRecord::Error(error_fid))
+                    }
+                    libc::FAN_EVENT_INFO_TYPE_PIDFD => {
+                        let error_fid = self
+                            .get_struct::<libc::fanotify_event_info_pidfd>(
+                                &buffer,
+                                current_event_offset,
+                            );
+                        Some(FanotifyInfoRecord::Pidfd(error_fid))
+                    }
+                    // Ignore unsupported events
+                    _ => None,
+                };
+
+                if let Some(record) = info_record {
+                    info_records.push(record);
+                }
+
+                remaining_len -= header.len as u32;
+                current_event_offset += header.len as usize;
+            }
+
+            // libc::fanotify_event_info_header
+
+            events.push((FanotifyEvent(metadata), info_records));
+            offset += metadata.event_len as usize;
+        }
+
+        Ok(events)
+    }
+
     /// Write an event response on the fanotify group.
     ///
     /// Returns a Result containing either `()` on success or errno otherwise.
@@ -423,4 +598,4 @@ impl From<Fanotify> for OwnedFd {
     fn from(value: Fanotify) -> Self {
         value.fd
     }
-}
+}

test/sys/test_fanotify.rs

@@ -3,7 +3,7 @@ use nix::errno::Errno;
 use nix::fcntl::AT_FDCWD;
 use nix::sys::fanotify::{
     EventFFlags, Fanotify, FanotifyResponse, InitFlags, MarkFlags, MaskFlags,
-    Response,
+    Response, FanotifyInfoRecord
 };
 use std::fs::{read_link, read_to_string, File, OpenOptions};
 use std::io::ErrorKind;
@@ -18,6 +18,7 @@ pub fn test_fanotify() {
 
     test_fanotify_notifications();
     test_fanotify_responses();
+    test_fanotify_notifications_with_info_records();
     test_fanotify_overflow();
 }
 
@@ -84,6 +85,65 @@ fn test_fanotify_notifications() {
     assert_eq!(path, tempfile);
 }
 
+fn test_fanotify_notifications_with_info_records() {
+    let group =
+        Fanotify::init(InitFlags::FAN_CLASS_NOTIF | InitFlags::FAN_REPORT_FID, EventFFlags::O_RDONLY)
+            .unwrap();
+    let tempdir = tempfile::tempdir().unwrap();
+    let tempfile = tempdir.path().join("test");
+    OpenOptions::new()
+        .write(true)
+        .create_new(true)
+        .open(&tempfile)
+        .unwrap();
+
+    group
+        .mark(
+            MarkFlags::FAN_MARK_ADD,
+            MaskFlags::FAN_OPEN | MaskFlags::FAN_MODIFY | MaskFlags::FAN_CLOSE,
+            AT_FDCWD,
+            Some(&tempfile),
+        )
+        .unwrap();
+
+    // modify test file
+    {
+        let mut f = OpenOptions::new().write(true).open(&tempfile).unwrap();
+        f.write_all(b"hello").unwrap();
+    }
+
+    let mut events = group.read_events_with_info_records().unwrap();
+    assert_eq!(events.len(), 1, "should have read exactly one event");
+    let (event, info_records) = events.pop().unwrap();
+    assert_eq!(info_records.len(), 1, "should have read exactly one info record");
+    assert!(event.check_version());
+    assert_eq!(
+        event.mask(),
+        MaskFlags::FAN_OPEN
+            | MaskFlags::FAN_MODIFY
+            | MaskFlags::FAN_CLOSE_WRITE
+    );
+
+    assert!(matches!(info_records[0], FanotifyInfoRecord::Fid { .. }), "info record should be an fid record");
+
+    // read test file
+    {
+        let mut f = File::open(&tempfile).unwrap();
+        let mut s = String::new();
+        f.read_to_string(&mut s).unwrap();
+    }
+
+    let mut events = group.read_events_with_info_records().unwrap();
+    assert_eq!(events.len(), 1, "should have read exactly one event");
+    let (event, info_records) = events.pop().unwrap();
+    assert_eq!(info_records.len(), 1, "should have read exactly one info record");
+    assert!(event.check_version());
+    assert_eq!(
+        event.mask(),
+        MaskFlags::FAN_OPEN | MaskFlags::FAN_CLOSE_NOWRITE
+    );
+}
+
 fn test_fanotify_responses() {
     let group =
         Fanotify::init(InitFlags::FAN_CLASS_CONTENT, EventFFlags::O_RDONLY)