From 604841c6c81608a7dfcfe05ab75fa0c7ede2a890 Mon Sep 17 00:00:00 2001
From: Benjamin Barenblat <bbaren@mit.edu>
Date: Sun, 21 Feb 2016 22:31:29 -0500
Subject: Implement symlink/readlink

---
 src/operations.cc   | 16 ++++++++++++++++
 src/posix_extras.cc | 18 ++++++++++++++++++
 src/posix_extras.h  | 10 ++++++++++
 3 files changed, 44 insertions(+)

diff --git a/src/operations.cc b/src/operations.cc
index e4e76b3..b1c568a 100644
--- a/src/operations.cc
+++ b/src/operations.cc
@@ -168,6 +168,19 @@ int Unlink(const char* c_path) {
   }
 }
 
+int Symlink(const char* const target, const char* const source) {
+  root_->SymLinkAt(target, EncodePath(source).c_str());
+  return 0;
+}
+
+int Readlink(const char* const path, char* const output,
+             const size_t output_size) {
+  const std::string target = root_->ReadLinkAt(EncodePath(path).c_str());
+  std::strncpy(output, target.c_str(), output_size);
+  output[output_size - 1] = '\0';
+  return 0;
+}
+
 int Mkdir(const char* const c_path, const mode_t mode) {
   const std::string path(c_path);
   if (path == "/") {
@@ -264,6 +277,9 @@ fuse_operations FuseOperations(File* const root) {
   result.release = CATCH_AND_RETURN_EXCEPTIONS(Release);
   result.unlink = CATCH_AND_RETURN_EXCEPTIONS(Unlink);
 
+  result.symlink = CATCH_AND_RETURN_EXCEPTIONS(Symlink);
+  result.readlink = CATCH_AND_RETURN_EXCEPTIONS(Readlink);
+
   result.mkdir = CATCH_AND_RETURN_EXCEPTIONS(Mkdir);
   result.opendir = CATCH_AND_RETURN_EXCEPTIONS(Opendir);
   result.readdir = CATCH_AND_RETURN_EXCEPTIONS(Readdir);
diff --git a/src/posix_extras.cc b/src/posix_extras.cc
index e7705a7..11db247 100644
--- a/src/posix_extras.cc
+++ b/src/posix_extras.cc
@@ -125,6 +125,19 @@ std::vector<std::uint8_t> File::Read(off_t offset, size_t bytes) const {
   return result;
 }
 
+std::string File::ReadLinkAt(const char* const path) const {
+  ValidatePath(path);
+  std::vector<char> result(64, '\0');
+  size_t bytes_read;
+
+  while ((bytes_read = static_cast<size_t>(CheckSyscall(readlinkat(
+              fd_, path, result.data(), result.size())))) == result.size()) {
+    // We filled the entire buffer.  There may be more data we missed.
+    result.resize(result.size() * 2);
+  }
+  return std::string(result.data(), result.data() + bytes_read);
+}
+
 void File::RenameAt(const char* old_path, const char* new_path) const {
   ValidatePath(old_path);
   ValidatePath(new_path);
@@ -136,6 +149,11 @@ void File::RmDirAt(const char* const path) const {
   CheckSyscall(unlinkat(fd_, path, AT_REMOVEDIR));
 }
 
+void File::SymLinkAt(const char* const target, const char* const source) const {
+  ValidatePath(source);
+  CheckSyscall(symlinkat(target, fd_, source));
+}
+
 void File::UnlinkAt(const char* const path) const {
   ValidatePath(path);
   CheckSyscall(unlinkat(fd_, path, 0));
diff --git a/src/posix_extras.h b/src/posix_extras.h
index 2976016..889175e 100644
--- a/src/posix_extras.h
+++ b/src/posix_extras.h
@@ -93,6 +93,11 @@ class File {
   // fewer bytes are returned.
   std::vector<std::uint8_t> Read(off_t, size_t) const;
 
+  // Reads the contents of a symbolic link.  The path to the symbolic link is
+  // interpreted relative to the file descriptor and must indeed be relative
+  // (i.e., it must not start with '/').
+  std::string ReadLinkAt(const char* path) const;
+
   // Renames a file from old_path to new_path.  Both paths are interpreted
   // relative to the file descriptor, and both must indeed be relative (i.e.,
   // they must not start with '/').
@@ -102,6 +107,11 @@ class File {
   // path must indeed be relative (i.e., it must not start with '/').
   void RmDirAt(const char* path) const;
 
+  // Creates a symlink at source pointing to target.  target is unvalidated.
+  // source is interpreted as a path relative to the file descriptor and must
+  // indeed be relative (i.e., it must not start with '/').
+  void SymLinkAt(const char* target, const char* source) const;
+
   // Removes the file at the path relative to the file descriptor.  The path
   // must indeed be relative (i.e., it must not start with '/').
   void UnlinkAt(const char* path) const;
-- 
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