Add a simple /bin/sysctl that wraps the files in /proc/sys.

AK/StringBuilder.cpp

@@ -40,12 +40,14 @@ void StringBuilder::appendf(const char* fmt, ...)
 ByteBuffer StringBuilder::to_byte_buffer()
 {
     m_buffer.trim(m_length);
-    return m_buffer;
+    return move(m_buffer);
 }
 
 String StringBuilder::build()
 {
-    return String((const char*)m_buffer.pointer(), m_length);
+    auto string = String((const char*)m_buffer.pointer(), m_length);
+    m_buffer.clear();
+    return string;
 }
 
 }

Kernel/sync.sh

@@ -43,6 +43,7 @@ cp -v ../Userland/touch mnt/bin/touch
 cp -v ../Userland/sync mnt/bin/sync
 cp -v ../Userland/more mnt/bin/more
 cp -v ../Userland/guitest mnt/bin/guitest
+cp -v ../Userland/sysctl mnt/bin/sysctl
 cp -v ../Terminal/Terminal mnt/bin/Terminal
 sh sync-local.sh
 cp -v kernel.map mnt/

Userland/.gitignore

@@ -22,3 +22,4 @@ touch
 sync
 more
 guitest
+sysctl

Userland/Makefile

@@ -19,7 +19,8 @@ OBJS = \
        mkdir.o \
        touch.o \
        more.o \
-       guitest.o
+       guitest.o \
+       sysctl.o
 
 APPS = \
        id \
@@ -43,7 +44,8 @@ APPS = \
        touch \
        sync \
        more \
-       guitest
+       guitest \
+       sysctl
 
 ARCH_FLAGS =
 STANDARD_FLAGS = -std=c++17 -nostdinc++ -nostdlib -nostdinc
@@ -129,6 +131,9 @@ more: more.o
 guitest: guitest.o
 	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
 
+sysctl: sysctl.o
+	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
+
 .cpp.o:
 	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
 

Userland/sysctl.cpp

@@ -0,0 +1,138 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <errno.h>
+#include <string.h>
+#include <getopt.h>
+#include <fcntl.h>
+#include <AK/AKString.h>
+#include <AK/StringBuilder.h>
+#include <AK/Vector.h>
+
+static bool flag_show_all = false;
+static int show_all();
+static int handle_var(const char*);
+
+static void usage()
+{
+    printf("usage: sysctl [-a] [variable[=value]]\n");
+}
+
+int main(int argc, char** argv)
+{
+    int opt;
+    while ((opt = getopt(argc, argv, "a")) != -1) {
+        switch (opt) {
+        case 'a':
+            flag_show_all = true;
+            break;
+        default:
+            usage();
+            return 0;
+        }
+    }
+
+    if (flag_show_all)
+        return show_all();
+
+    if (optind >= argc) {
+        usage();
+        return 0;
+    }
+
+    const char* var = argv[optind];
+
+    return handle_var(var);
+}
+
+int show_all()
+{
+    DIR* dirp = opendir("/proc/sys");
+    if (!dirp) {
+        perror("opendir");
+        return 1;
+    }
+    char pathbuf[256];
+
+    while (auto* de = readdir(dirp)) {
+        if (de->d_name[0] == '.')
+            continue;
+        sprintf(pathbuf, "/proc/sys/%s", de->d_name);
+        int fd = open(pathbuf, O_RDONLY);
+        if (fd < 0) {
+            perror("open");
+            continue;
+        }
+        char buffer[1024];
+        int nread = read(fd, buffer, sizeof(buffer));
+        close(fd);
+        if (nread < 0) {
+            perror("read");
+            continue;
+        }
+        buffer[nread] = '\0';
+        printf("%s = %s", de->d_name, buffer);
+        if (nread && buffer[nread - 1] != '\n')
+            printf("\n");
+    }
+    closedir(dirp);
+    return 0;
+}
+
+static String read_var(const String& name)
+{
+    StringBuilder builder;
+    builder.append("/proc/sys/");
+    builder.append(name);
+    auto path = builder.build();
+    int fd = open(path.characters(), O_RDONLY);
+    if (fd < 0) {
+        perror("open");
+        exit(1);
+    }
+    char buffer[1024];
+    int nread = read(fd, buffer, sizeof(buffer));
+    close(fd);
+    if (nread < 0) {
+        perror("read");
+        exit(1);
+    }
+    return String(buffer, nread, Chomp);
+}
+
+static void write_var(const String& name, const String& value)
+{
+    StringBuilder builder;
+    builder.append("/proc/sys/");
+    builder.append(name);
+    auto path = builder.build();
+    int fd = open(path.characters(), O_WRONLY);
+    if (fd < 0) {
+        perror("open");
+        exit(1);
+    }
+    int nwritten = write(fd, value.characters(), value.length());
+    if (nwritten < 0) {
+        perror("read");
+        exit(1);
+    }
+    close(fd);
+}
+
+int handle_var(const char* var)
+{
+    String spec(var, Chomp);
+    auto parts = spec.split('=');
+    String variable_name = parts[0];
+    bool is_write = parts.size() > 1;
+
+    if (!is_write) {
+        printf("%s = %s\n", variable_name.characters(), read_var(variable_name).characters());
+        return 0;
+    }
+
+    printf("%s = %s", variable_name.characters(), read_var(variable_name).characters());
+    write_var(variable_name, parts[1]);
+    printf(" -> %s\n", read_var(variable_name).characters());
+    return 0;
+}