src/pxar/fuse.rs: impl lookup callback for fuse

The lookup call checks if the given filename is found in the directory referenced
by the i-node by calclulating the filenames hash and looking it up in the
directories goodbye table.
If found, the entries parameters are returned.
In order to be able to lookup the parent offset by a given file offset in the
readdir callback, this also stores the corresponding values in a HashMap.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>

src/pxar/fuse.rs

@@ -2,8 +2,9 @@
 //!
 //! Allows to mount the archive as read-only filesystem to inspect its contents.
 
-use std::ffi::{CString, OsStr};
+use std::collections::HashMap;
 use std::convert::TryFrom;
+use std::ffi::{CStr, CString, OsStr};
 use std::fs::File;
 use std::os::unix::ffi::OsStrExt;
 use std::io::{BufReader, Read, Seek};
@@ -11,6 +12,7 @@ use std::path::Path;
 use std::sync::Mutex;
 
 use failure::{bail, format_err, Error};
+use lazy_static::lazy_static;
 use libc;
 use libc::{c_char, c_int, c_void, size_t};
 
@@ -29,6 +31,16 @@ use super::format_definition::{PxarAttributes, PxarGoodbyeItem};
 const FUSE_ROOT_ID: u64 = 1;
 
 const GOODBYE_ITEM_SIZE: u64 = std::mem::size_of::<PxarGoodbyeItem>() as u64;
+lazy_static! {
+    /// HashMap holding the mapping from the child offsets to their parent
+    /// offsets.
+    ///
+    /// In order to include the parent directory entry '..' in the response for
+    /// readdir callback, this mapping is needed.
+    /// Calling the lookup callback will insert the offsets into the HashMap.
+    static ref CHILD_PARENT: Mutex<HashMap<u64, u64>> = Mutex::new(HashMap::new());
+}
+
 /// Callback function for `super::decoder::Decoder`.
 ///
 /// At the moment, this is only needed to satisfy the `SequentialDecoder`.
@@ -56,6 +68,7 @@ extern "C" {
     fn fuse_session_destroy(session: ConstPtr);
     fn fuse_reply_attr(req: Request, attr: Option<&libc::stat>, timeout: f64) -> c_int;
     fn fuse_reply_err(req: Request, errno: c_int) -> c_int;
+    fn fuse_reply_entry(req: Request, entry: Option<&EntryParam>) -> c_int;
     fn fuse_req_userdata(req: Request) -> MutPtr;
 }
 
@@ -307,11 +320,62 @@ extern "C" fn destroy(decoder: MutPtr) {
     }
 }
 
-extern "C" fn lookup(req: Request, parent: u64, _name: StrPtr) {
-    run_in_context(req, parent, |_decoder, _ino_offset| {
-        // code goes here
+/// FUSE entry for fuse_reply_entry in lookup callback
+#[repr(C)]
+struct EntryParam {
+    inode: u64,
+    generation: u64,
+    attr: libc::stat,
+    attr_timeout: f64,
+    entry_timeout: f64,
+}
 
-        Err(libc::ENOENT)
+/// Lookup `name` in the directory referenced by `parent` inode.
+///
+/// Inserts also the child and parent file offset in the hashmap to quickly
+/// obtain the parent offset based on the child offset.
+extern "C" fn lookup(req: Request, parent: u64, name: StrPtr) {
+    let filename = unsafe { CStr::from_ptr(name) };
+    let hash = super::format_definition::compute_goodbye_hash(filename.to_bytes());
+
+    run_in_context(req, parent, |mut decoder, ino_offset| {
+        let goodbye_table = decoder.goodbye_table(None, ino_offset + GOODBYE_ITEM_SIZE).map_err(|_| libc::EIO)?;
+
+        let (_item, start, end) = goodbye_table
+            .iter()
+            .find(|(e, _, _)| e.hash == hash)
+            .ok_or(libc::ENOENT)?;
+
+        let (mut attr, _) = stat(&mut decoder, *start)?;
+        let offset = if attr.st_mode & libc::S_IFMT == libc::S_IFDIR {
+            *end - GOODBYE_ITEM_SIZE
+        } else {
+            *start
+        };
+        let inode = if offset == decoder.root_end_offset() - GOODBYE_ITEM_SIZE {
+            FUSE_ROOT_ID
+        } else {
+            offset
+        };
+        attr.st_ino = inode;
+
+        let e = EntryParam {
+            inode,
+            generation: 1,
+            attr,
+            attr_timeout: std::f64::MAX,
+            entry_timeout: std::f64::MAX,
+        };
+
+        // Update the parent for this child entry. Used to get parent offset if
+        // only child offset is known.
+        CHILD_PARENT
+            .lock()
+            .map_err(|_| libc::EIO)?
+            .insert(offset, ino_offset);
+        let _res = unsafe { fuse_reply_entry(req, Some(&e)) };
+
+        Ok(())
     });
 }