liblinux++

commit 01f91fef9e95f76fa044f6fe4a92bcd8a5fb61dc
parent d9b07a955ad27b4143c3f34b18b1130957718d50
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Fri,  9 Jan 2026 00:38:14 +0000

ls: fix repeated output

Diffstat:
M
linux.hpp
 | 
7
+++++++
M
ls.cpp
 | 
38
++++++++++++++++++++++++++------------

2 files changed, 33 insertions(+), 12 deletions(-)
diff --git a/linux.hpp b/linux.hpp
@@ -75,6 +75,10 @@ struct span
 	{
 		return begin() + size();
 	}
+	T& operator[](size_t n)
+	{
+		return ptr[n];
+	}
 private:
 	T* ptr = nullptr;
 	size_t len = 0;
@@ -172,6 +176,9 @@ struct [[gnu::packed]] linux_dirent64 {
 	off64_t        d_off;    /* Not an offset; see getdents() */
 	unsigned short d_reclen; /* Size of this dirent */
 	unsigned char  d_type;   /* File type */
+
+	linux_dirent64* next() noexcept { return reinterpret_cast<linux_dirent64*>(reinterpret_cast<char*>(this) + d_reclen); }
+	char* name() noexcept { return reinterpret_cast<char*>(this) + sizeof(*this); }
 };
 extern syscall_result<size_t> getdents64(file dir, span<char> buffer) noexcept;
 
diff --git a/ls.cpp b/ls.cpp
@@ -1,31 +1,45 @@
 #include "linux.hpp"
 
+template <typename T>
+struct spanstack
+{
+	spanstack(span<T> st) : storage{st} {}
+
+	bool empty() const noexcept { return not n; }
+	bool full() const noexcept { return n == storage.size(); }
+	span<T const> data() noexcept { return {(T const*)storage.begin(), n}; }
+	void push_back(T const& v) noexcept
+	{
+		assert(not full());
+		storage[n++] = v;
+	}
+private:
+	span<T> storage;
+	size_t n = 0;
+};
+
 int main()
 {
 	auto dir = openat(AT_FDCWD, ".", O_RDONLY, 0);
 	assert(dir);
 
 	alignas(linux_dirent64) char buf[256];
-	span<char const> ios[sizeof(buf)/sizeof(linux_dirent64)];
+	span<char const> ios_storage[sizeof(buf)/sizeof(linux_dirent64)];
 	for (;;)
 	{
-		unsigned n_io = 0;
+		spanstack ios{span{ios_storage}};
 		auto res = getdents64(*dir, buf);
-		size_t n = *res;
-
-		if (!n)
+		void* const end = buf + *res;
+		if (end == buf)
 			break;
 
-		for (size_t i = 0; i + sizeof(linux_dirent64) < n;)
+		for (auto ent = reinterpret_cast<linux_dirent64*>(buf); ent != end; ent = ent->next())
 		{
-			auto e = reinterpret_cast<linux_dirent64*>(buf + i);
-			char* const name = buf + i + sizeof(linux_dirent64);
+			char* const name = ent->name();
 			size_t len = c_str{name}.length();
 			name[len++] = '\n';
-			ios[n_io++] = span<char const>{name, len};
-			i += e->d_reclen;
-			break;
+			ios.push_back({name, len});
 		}
-		*write(stdout, ios);
+		*write(stdout, ios.data());
 	}
 }