feat(userspace): add demo ring-3 programs

user/counter.c

@@ -0,0 +1,18 @@
+#include "ulib.h"
+
+int main(void)
+{
+    long pid = userGetpid();
+
+    for (int step = 0; step < 5; step++) {
+        print("counter: pid=");
+        printDec(pid);
+        print(" step=");
+        printDec(step);
+        print("\n");
+        userSleep(30);
+    }
+
+    print("counter: finished counting\n");
+    return 0;
+}

user/fileread.c

@@ -0,0 +1,77 @@
+#include "ulib.h"
+#include "fs.h"
+
+static const char* motdPath = "/etc/motd.txt";
+static const char* notePath = "/tmp/note.txt";
+
+int main(void)
+{
+    print("fileread: start, pid=");
+    printDec(userGetpid());
+    print("\n");
+
+    FbStat st;
+    if (userStat(motdPath, &st) == 0) {
+        print("fileread: stat ");
+        print(motdPath);
+        print(" size=");
+        printDec((long)st.size);
+        print("\n");
+    } else {
+        print("fileread: stat failed\n");
+    }
+
+    int fd = (int)userOpen(motdPath, oReadOnly);
+    if (fd < 0) {
+        print("fileread: open failed\n");
+        return 1;
+    }
+
+    print("fileread: --- begin ");
+    print(motdPath);
+    print(" ---\n");
+    char buffer[128];
+    long n;
+    while ((n = userRead(fd, buffer, sizeof(buffer))) > 0)
+        userWrite(1, buffer, (unsigned long)n);
+    print("fileread: --- end ---\n");
+
+    userLseek(fd, 0, seekSet);
+    n = userRead(fd, buffer, 16);
+    print("fileread: lseek reread first bytes: ");
+    userWrite(1, buffer, (unsigned long)n);
+    print("\n");
+    userClose(fd);
+
+    int wfd = (int)userOpen(notePath, oReadWrite | oCreate | oTrunc);
+    if (wfd < 0) {
+        print("fileread: tmpfs open failed\n");
+        return 2;
+    }
+    const char* payload = "frostbyte-tmpfs-rw-ok\n";
+    userWrite(wfd, payload, stringLength(payload));
+    userLseek(wfd, 0, seekSet);
+    char readback[64];
+    long rn = userRead(wfd, readback, sizeof(readback));
+    print("fileread: tmpfs read back: ");
+    userWrite(1, readback, (unsigned long)rn);
+    userClose(wfd);
+
+    print("fileread: listing /etc via getdents:\n");
+    int dfd = (int)userOpen("/etc", oReadOnly);
+    if (dfd >= 0) {
+        FbDirent entries[8];
+        long bytes = userGetdents(dfd, entries, sizeof(entries));
+        long records = bytes / (long)sizeof(FbDirent);
+        for (long i = 0; i < records; i++) {
+            print("  ");
+            print(entries[i].name);
+            print(entries[i].type == fsTypeDir ? "/" : "");
+            print("\n");
+        }
+        userClose(dfd);
+    }
+
+    print("fileread: done\n");
+    return 0;
+}

user/hello.c

@@ -0,0 +1,13 @@
+#include "ulib.h"
+
+int main(void)
+{
+    print("hello: greetings from ring 3, pid=");
+    printDec(userGetpid());
+    print("\n");
+
+    userYield();
+
+    print("hello: resumed after yield, exiting cleanly\n");
+    return 7;
+}

user/sbrktest.c

@@ -0,0 +1,27 @@
+#include "ulib.h"
+
+#define blockBytes 8192
+
+int main(void)
+{
+    print("sbrktest: pid=");
+    printDec(userGetpid());
+    print(" requesting 8192 bytes via sbrk\n");
+
+    char* block = (char*)userSbrk(blockBytes);
+
+    for (int i = 0; i < blockBytes; i++)
+        block[i] = (char)(i & 0x7F);
+
+    int intact = 1;
+    for (int i = 0; i < blockBytes; i++)
+        if (block[i] != (char)(i & 0x7F))
+            intact = 0;
+
+    if (intact)
+        print("sbrktest: heap page write and read-back verified OK\n");
+    else
+        print("sbrktest: heap verification FAILED\n");
+
+    return 0;
+}