Improve FUSE init configuration

libparsec/crates/platform_mountpoint/src/unix/filesystem.rs

@@ -3,6 +3,7 @@
 use std::{
     ffi::OsStr,
     sync::{Arc, Mutex},
+    time::Duration,
 };
 
 use libparsec_client::workspace::{
@@ -216,8 +217,90 @@ impl fuser::Filesystem for Filesystem {
         // see https://libfuse.github.io/doxygen/structfuse__conn__info.html
         config: &mut fuser::KernelConfig,
     ) -> Result<(), libc::c_int> {
-        // Try to enable readdirplus optimisation, if it's not possible we fallback on regular readdir
-        let _ = config.add_capabilities(fuser::consts::FUSE_DO_READDIRPLUS);
+        // See libfuse & Linux documentation for a description of the capabilities.
+        // See:
+        // - https://github.com/torvalds/linux/blob/e32cde8d2bd7d251a8f9b434143977ddf13dcec6/include/uapi/linux/fuse.h#L376-L428
+        // - https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L158
+
+        // Here the general idea is to follow libfuse3's default configuration on what
+        //    should be enabled.
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/lib/fuse_lowlevel.c#L2087-L2108
+
+        // Note Fuser already set the following capabilities:
+        // - On Linux: FUSE_ASYNC_READ | FUSE_BIG_WRITES | FUSE_MAX_PAGES
+        // - On macOS: FUSE_ASYNC_READ | FUSE_CASE_INSENSITIVE | FUSE_VOL_RENAME | FUSE_XTIMES | FUSE_MAX_PAGES
+
+        // `FUSE_POSIX_LOCKS` (remote locking support) is not enabled since we don't
+        // implement `getlk()` & `setlk()` handlers.
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L179
+
+        // `FUSE_FLOCK_LOCKS` is not enabled since we don't implement `flock()` handler.
+        // Instead we rely on in-kernel POSIX lock emulation.
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L246
+
+        // `FUSE_ASYNC_DIO` is not enabled since we don't do direct I/O.
+        // See:
+        // - https://www.kernel.org/doc/html/latest/filesystems/fuse-io.html
+        // - https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L322
+
+        // Do not send separate SETATTR request before open(O_TRUNC).
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L188
+        config
+            .add_capabilities(fuser::consts::FUSE_ATOMIC_O_TRUNC)
+            .expect("Capability available");
+
+        // Support IOCTL on directories.
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L253
+        config
+            .add_capabilities(fuser::consts::FUSE_IOCTL_DIR)
+            .expect("Capability available");
+
+        // Tell FUSE the data may change without going through the filesystem, hence attributes
+        // validity should be checked on each access (leading to `getattr()` on timeout).
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L275
+        config
+            .add_capabilities(fuser::consts::FUSE_AUTO_INVAL_DATA)
+            .expect("Capability available");
+
+        // Enable `readdirplus` support (readdir + lookup in one a single go).
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L283
+        config
+            .add_capabilities(fuser::consts::FUSE_DO_READDIRPLUS)
+            .expect("Capability available");
+
+        // Adaptative readdirplus optimization support: still use readdir when lookup is
+        // has already been done by the previous readdirplus.
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L311
+        config
+            .add_capabilities(fuser::consts::FUSE_READDIRPLUS_AUTO)
+            .expect("Capability available");
+
+        // TODO: `FUSE_SPLICE_READ` seems to require `write_buf()` to be implemented, which is
+        //       not even exposed in fuser !
+        // Allow splice operations (see `man 2 splice`, basically kernal space page-based operations)
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L216
+        config
+            .add_capabilities(fuser::consts::FUSE_SPLICE_WRITE)
+            .expect("Capability available");
+        config
+            .add_capabilities(fuser::consts::FUSE_SPLICE_MOVE)
+            .expect("Capability available");
+        config
+            .add_capabilities(fuser::consts::FUSE_SPLICE_READ)
+            .expect("Capability available");
+
+        // Allow parallel lookups and readdir on any given folder (default is serialized).
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L354
+        config
+            .add_capabilities(fuser::consts::FUSE_PARALLEL_DIROPS)
+            .expect("Capability available");
+
+        // Inform the Kernel about the granularity of the timestamps supported by our filesystem.
+        // See https://github.com/libfuse/libfuse/blob/2aeef499b84b596608181f9b48d589c4f8ffe24a/include/fuse_common.h#L609-L622
+        config
+            .set_time_granularity(Duration::from_micros(1))
+            .expect("Valid granularity");
+
         Ok(())
     }
 
@@ -1086,6 +1169,17 @@ impl fuser::Filesystem for Filesystem {
             offset,
             data.len(),
         );
+        let log = std::path::PathBuf::from(format!(
+            "/home/emmanuel/projects/parsec-cloud/fs_{ino:x}_{offset:x}.log"
+        ));
+        std::fs::File::options()
+            .create(true)
+            .append(true)
+            .write(true)
+            .open(log)
+            .unwrap()
+            .write_all(data)
+            .unwrap();
         let reply = reply_on_drop_guard!(reply, fuser::ReplyWrite);
         let data = data.to_vec();
 
@@ -1096,6 +1190,13 @@ impl fuser::Filesystem for Filesystem {
             let offset = u64::try_from(offset).expect("Offset is negative");
             match ops.fd_write(fd, offset, &data).await {
                 Ok(written) => {
+                    log::debug!(
+                        "[FUSE] write DONE (ino: {:#x?}, fh: {}, offset: {}, data.len(): {})",
+                        ino,
+                        fh,
+                        offset,
+                        data.len(),
+                    );
                     reply.manual().written(written as u32);
                 }
                 Err(err) => match err {