userspace: Add basic find utility

This is mostly working but is missing -exec and -ok support. It can
search files though :^)

userspace/programs/find/main.cpp

@@ -0,0 +1,137 @@
+#include "Node.h"
+#include "Token.h"
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+
+enum class LinkMode
+{
+	Physical, Logical, Half
+};
+
+const char* g_argv0 { nullptr };
+
+static dev_t s_first_st_dev { 0 };
+
+static void recurse_path(int fd, const char* name, const char* path, Node* node, LinkMode link_mode)
+{
+	int stat_flag = 0;
+	if (link_mode == LinkMode::Physical)
+		stat_flag = AT_SYMLINK_NOFOLLOW;
+	else if (link_mode == LinkMode::Half && (fd != AT_FDCWD))
+		stat_flag = AT_SYMLINK_NOFOLLOW;
+
+	struct stat st;
+	if (fstatat(fd, name, &st, stat_flag) == -1)
+	{
+		fprintf(stderr, "%s: '%s': %s\n", g_argv0, path, strerror(errno));
+		return;
+	}
+
+	if (fd == AT_FDCWD)
+		s_first_st_dev = st.st_dev;
+
+	if (g_mount_specified && st.st_dev != s_first_st_dev)
+		return;
+
+	if (!g_depth_specified || !S_ISDIR(st.st_mode))
+		evaluate_node(node, path, st);
+
+	if (S_ISDIR(st.st_mode) && (!g_prune_specified || g_depth_specified) && (!g_xdev_specified || st.st_dev == s_first_st_dev))
+	{
+		int open_flag = stat_flag ? O_NOFOLLOW : 0;
+
+		int dirfd = openat(fd, name, O_RDONLY | O_DIRECTORY | open_flag);
+		if (dirfd < 0)
+			fprintf(stderr, "%s: '%s': %s\n", g_argv0, path, strerror(errno));
+
+		DIR* dirp = nullptr;
+		if ((dirfd >= 0) && (dirp = fdopendir(dirfd)))
+		{
+			char buffer[PATH_MAX];
+
+			char* buffer_end = stpcpy(buffer, path);
+			if (*path && buffer_end[-1] != '/')
+				*buffer_end++ = '/';
+
+			dirent* dirent;
+			while ((errno = 0) || (dirent = readdir(dirp)))
+			{
+				if (strcmp(dirent->d_name, ".") == 0 || strcmp(dirent->d_name, "..") == 0)
+					continue;
+				strcpy(buffer_end, dirent->d_name);
+				recurse_path(dirfd, dirent->d_name, buffer, node, link_mode);
+			}
+
+			if (errno)
+				fprintf(stderr, "%s: '%s': %s\n", g_argv0, path, strerror(errno));
+
+			closedir(dirp);
+		}
+
+		if (dirp == nullptr && dirfd >= 0)
+		{
+			fprintf(stderr, "%s: '%s': %s\n", g_argv0, path, strerror(errno));
+			close(dirfd);
+		}
+	}
+
+	if (g_depth_specified && S_ISDIR(st.st_mode))
+		evaluate_node(node, path, st);
+}
+
+int main(int argc, char** argv)
+{
+	g_argv0 = argv[0];
+
+	LinkMode link_mode { LinkMode::Physical };
+
+	int idx = 1;
+	for (; idx < argc; idx++)
+	{
+		if (argv[idx][0] != '-')
+			break;
+		else if (strcmp(argv[idx], "-P") == 0)
+			link_mode = LinkMode::Physical;
+		else if (strcmp(argv[idx], "-L") == 0)
+			link_mode = LinkMode::Logical;
+		else if (strcmp(argv[idx], "-H") == 0)
+			link_mode = LinkMode::Half;
+		else if (strcmp(argv[idx], "--help") == 0)
+		{
+			fprintf(stderr, "usage: %s [-P|-L|-H] PATH... [EXPRESSION...]\n", argv[0]);
+			fprintf(stderr, "  find files based on expressions\n");
+			fprintf(stderr, "OPTIONS:\n");
+			fprintf(stderr, "  -P          never follow symbolic links\n");
+			fprintf(stderr, "  -L          follow symbolic links\n");
+			fprintf(stderr, "  -H          only follow symbolic links in PATH...\n");
+			fprintf(stderr, "      --help  show this message and exit\n");
+			return 0;
+		}
+		else break;
+	}
+
+	if (idx < argc && strcmp(argv[idx], "--") == 0)
+		idx++;
+
+	constexpr auto is_path_start = [](char ch) {
+		return ch != '-' && ch != '!' && ch != '(';
+	};
+
+	size_t path_count = 0;
+	while (idx + path_count < static_cast<size_t>(argc) && is_path_start(argv[idx + path_count][0]))
+		path_count++;
+
+	auto tokens = tokenize(&argv[idx + path_count]);
+	auto* node = compile_tokens(tokens.span());
+
+	if (path_count == 0)
+		recurse_path(AT_FDCWD, ".", ".", node, link_mode);
+	else for (size_t i = 0; i < path_count; i++)
+		recurse_path(AT_FDCWD, argv[idx + i], argv[idx + i], node, link_mode);
+
+	return 0;
+}