From 271b2985480b13a4e2728ac57f09651f1b1d87eb Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Tue, 4 Mar 2025 10:50:39 -0800
Subject: [PATCH] [WasmFS] Create public `wasmfs_mount` function
We already had `wasmfs_unmount` so it seems logical we should have this
one too.
This is designed to replace `wasmfs_create_directory` which has a rather
misleading name.
I have left `wasmfs_create_directory` around for now but is simply
combination of `mkdir` + `mount` (which is essentially what is was
doing already).
This change ends up simplifying `doMkdir` which no longer needs to take
a backend argument.
---
src/lib/libwasmfs.js | 2 +-
system/include/emscripten/wasmfs.h | 8 ++--
system/lib/wasmfs/js_api.cpp | 15 -------
system/lib/wasmfs/syscalls.cpp | 71 ++++++++++++++++++------------
tools/link.py | 2 +-
5 files changed, 50 insertions(+), 48 deletions(-)
diff --git a/src/lib/libwasmfs.js b/src/lib/libwasmfs.js
index 63a14510767bd..a665f431b56b8 100644
--- a/src/lib/libwasmfs.js
+++ b/src/lib/libwasmfs.js
@@ -348,7 +348,7 @@ addToLibrary({
}
#endif
var backendPointer = type.createBackend(opts);
- return FS.handleError(withStackSave(() => __wasmfs_mount(stringToUTF8OnStack(mountpoint), backendPointer)));
+ return FS.handleError(withStackSave(() => _wasmfs_mount(stringToUTF8OnStack(mountpoint), backendPointer)));
},
unmount: (mountpoint) => (
FS.handleError(withStackSave(() => _wasmfs_unmount(stringToUTF8OnStack(mountpoint))))
diff --git a/system/include/emscripten/wasmfs.h b/system/include/emscripten/wasmfs.h
index f7025dc6eb6cb..b3839e26d1dda 100644
--- a/system/include/emscripten/wasmfs.h
+++ b/system/include/emscripten/wasmfs.h
@@ -29,11 +29,13 @@ backend_t wasmfs_get_backend_by_fd(int fd);
// TODO: Remove this function so that only directories can be mounted.
int wasmfs_create_file(const char* pathname __attribute__((nonnull)), mode_t mode, backend_t backend);
-// Creates a new directory using a specific backend.
-// Returns 0 on success like `mkdir`, or a negative value on error.
-// TODO: Add an alias with wasmfs_mount.
+// Legacy function. This function works like `mkdir` + `wasmfs_mount`.
int wasmfs_create_directory(const char* path __attribute__((nonnull)), mode_t mode, backend_t backend);
+// Mount a backend at a given location in the filesystem
+// `path` must be an existing directory.
+int wasmfs_mount(const char* path __attribute__((nonnull)), backend_t backend);
+
// Unmounts the directory (Which must be a valid mountpoint) at a specific path.
// Returns 0 on success, or a negative value on error.
int wasmfs_unmount(const char* path __attribute__((nonnull)));
diff --git a/system/lib/wasmfs/js_api.cpp b/system/lib/wasmfs/js_api.cpp
index bcf3be01c5c9f..08b605a86d7ab 100644
--- a/system/lib/wasmfs/js_api.cpp
+++ b/system/lib/wasmfs/js_api.cpp
@@ -277,21 +277,6 @@ int _wasmfs_lstat(const char* path, struct stat* statBuf) {
return __syscall_lstat64((intptr_t)path, (intptr_t)statBuf);
}
-// The legacy JS API requires a mountpoint to already exist, so WasmFS will
-// attempt to remove the target directory if it exists before replacing it with
-// a mounted directory.
-int _wasmfs_mount(const char* path, ::backend_t created_backend) {
- int err = __syscall_rmdir((intptr_t)path);
-
- // The legacy JS API mount requires the directory to already exist, but we
- // will also allow it to be missing.
- if (err && err != -ENOENT) {
- return err;
- }
-
- return wasmfs_create_directory(path, 0777, created_backend);
-}
-
// Helper method that identifies what a path is:
// ENOENT - if nothing exists there
// EISDIR - if it is a directory
diff --git a/system/lib/wasmfs/syscalls.cpp b/system/lib/wasmfs/syscalls.cpp
index 64932128d19ad..c5de6fcedaceb 100644
--- a/system/lib/wasmfs/syscalls.cpp
+++ b/system/lib/wasmfs/syscalls.cpp
@@ -597,8 +597,7 @@ int __syscall_mknodat(int dirfd, intptr_t path, int mode, int dev) {
OpenReturnMode::Nothing);
}
-static int
-doMkdir(path::ParsedParent parsed, int mode, backend_t backend = NullBackend) {
+static int doMkdir(path::ParsedParent parsed, int mode) {
if (auto err = parsed.getError()) {
return err;
}
@@ -624,41 +623,57 @@ doMkdir(path::ParsedParent parsed, int mode, backend_t backend = NullBackend) {
return -EACCES;
}
- // By default, the backend that the directory is created in is the same as
- // the parent directory. However, if a backend is passed as a parameter,
- // then that backend is used.
- if (!backend) {
- backend = parent->getBackend();
+ if (!lockedParent.insertDirectory(childName, mode)) {
+ // TODO Receive a specific error code, and report it here. For now, report
+ // a generic error.
+ return -EIO;
}
- if (backend == parent->getBackend()) {
- if (!lockedParent.insertDirectory(childName, mode)) {
- // TODO Receive a specific error code, and report it here. For now, report
- // a generic error.
- return -EIO;
- }
- } else {
- auto created = backend->createDirectory(mode);
- if (!created) {
- // TODO Receive a specific error code, and report it here. For now, report
- // a generic error.
- return -EIO;
- }
- [[maybe_unused]] bool mounted = lockedParent.mountChild(childName, created);
- assert(mounted);
+ // TODO: Check that the insertion is successful.
+
+ return 0;
+}
+
+int wasmfs_mount(const char* path, backend_t backend) {
+ path::ParsedParent parsed = path::parseParent(path);
+ if (auto err = parsed.getError()) {
+ return err;
}
+ auto& [parent, childNameView] = parsed.getParentChild();
+ auto lockedParent = parent->locked();
+ std::string childName(childNameView);
- // TODO: Check that the insertion is successful.
+ // Child must exist and must be directory
+ auto child = lockedParent.getChild(childName);
+ if (!child) {
+ return -EEXIST;
+ }
+ if (!child->dynCast<Directory>()) {
+ return -ENOTDIR;
+ }
+
+ auto created = backend->createDirectory(0777);
+ if (!created) {
+ // TODO Receive a specific error code, and report it here. For now, report
+ // a generic error.
+ return -EIO;
+ }
+ [[maybe_unused]] bool mounted = lockedParent.mountChild(childName, created);
+ assert(mounted);
return 0;
}
-// This function is exposed to users and allows users to specify a particular
-// backend that a directory should be created within.
-int wasmfs_create_directory(char* path, int mode, backend_t backend) {
- static_assert(std::is_same_v<decltype(doMkdir(0, 0, 0)), int>,
+// Legacy function, use wasmfs_mount instead.
+int wasmfs_create_directory(const char* path, int mode, backend_t backend) {
+ static_assert(std::is_same_v<decltype(doMkdir(0, 0)), int>,
"unexpected conversion from result of doMkdir to int");
- return doMkdir(path::parseParent(path), mode, backend);
+ int rtn = doMkdir(path::parseParent(path), mode);
+ if (rtn != 0) {
+ return rtn;
+ }
+
+ return wasmfs_mount(path, backend);
}
// TODO: Test this.
diff --git a/tools/link.py b/tools/link.py
index 9440e8908a858..314a3b70895cb 100644
--- a/tools/link.py
+++ b/tools/link.py
@@ -1265,7 +1265,7 @@ def phase_linker_setup(options, linker_args): # noqa: C901, PLR0912, PLR0915
'emscripten_builtin_memalign',
'wasmfs_create_file',
'wasmfs_unmount',
- '_wasmfs_mount',
+ 'wasmfs_mount',
'_wasmfs_read_file',
'_wasmfs_write_file',
'_wasmfs_open',