Makefile now correctly calls i386 QEMU instead of x86_64

Changed the type for block addresses from size_t to uint16_t.

Added the '%c' conversion specifier to vsprintf(), so that it can now
output individual characters passed as arguments.

Added a an errno.h header containing a list of commonly used error
codes, as well as a basic strerror() routine to fetch corresponding
human-readable strings from a table.

Implemented barebones floppy driver. Currently lacking many (essential)
features, see TODO notes in floppy.c for more details.

Buffer structs now have a b_present flag to indicate whether or not the
data section is populated, as well as a b_wait element, as a queue for
any tasks waiting on the buffer. All tasks waiting on a block wait in
this queue, however, the task that originally called the driver to read,
may wait in a separate queue maintained by the driver. This system may
change in the future, and will likely depend on how head scheduling is
implemented in the driver.

The buffer_get_block() routine is now publically available in
kernel/fs.h. It can be called to retrieve a block from the buffer cache
(if readily available), or from the specified block device otherwise.
This routine returns a pointer to the buffer containing the cache.

The block_read() function now passes arguments and return values to the
floppy driver regardless of the device specified. The block_write()
function now indicates an error condition by setting b_device to zero in
the allocated buffer structure, as no devices with write functionality
currently exist. This behaviour will be updated in future, as more block
devices are added.

The mount_root() function has been modified to call buffer_get_block(),
instead of calling block_read() directly. As of now, nothing should call
block_read() or block_write() directly, as those functions are intended
for use by the buffer subsystem only.

17 files changed, 672 insertions, 76 deletions

diff --git a/Makefile b/Makefile
index fdd1362..c107ea1 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@ clean:
 	rm -f $(TARGET)
 
 run: $(TARGET)
-	qemu-system-x86_64 -s -kernel $(TARGET) -serial stdio
-	#qemu-system-x86_64 -s -S -kernel $(TARGET) -drive file=hd.img,format=raw
+	qemu-system-i386 -s -kernel $(TARGET) -fda floppy.img -serial stdio
+	#qemu-system-i386 -s -S -kernel $(TARGET) -drive file=hd.img,format=raw
 
 .FORCE:
diff --git a/floppy.img b/floppy.img
new file mode 100644
index 0000000..b399a80
--- /dev/null
+++ b/floppy.img
diff --git a/include/kernel/fd.h b/include/kernel/fd.h
new file mode 100644
index 0000000..07cf454
--- /dev/null
+++ b/include/kernel/fd.h
@@ -0,0 +1,12 @@
+#ifndef _FD_H
+#define _FD_H
+
+#include <kernel/fs.h>
+#include <stdint.h>
+#include <sys/types.h>
+
+void fd_init(void);
+
+void fd_block_read(struct buffer*);
+
+#endif
diff --git a/include/kernel/fs.h b/include/kernel/fs.h
index 4ec4de1..1b4ed24 100644
--- a/include/kernel/fs.h
+++ b/include/kernel/fs.h
@@ -52,16 +52,20 @@ struct m_inode {
 
 struct buffer {
   void *b_data;
+  int b_present;
   uint16_t b_device;
   uint16_t b_block;
+  struct task_struct *b_wait;
   struct buffer *b_next;
   struct buffer *b_prev;
-} __attribute__((packed));
+};
 
 extern struct super_block sblocks[NRSUPER];
 
-int block_read(void*, size_t);
-int block_write(void*, size_t);
+void block_read(struct buffer*);
+void block_write(struct buffer*);
+
+struct buffer *buffer_get_block(uint16_t, uint16_t);
 
 void mount_root(void);
 
diff --git a/include/string.h b/include/string.h
index d2f738b..88a6ac4 100644
--- a/include/string.h
+++ b/include/string.h
@@ -33,5 +33,6 @@ char *strpbrk(const char*, const char*);
 char *strstr(const char*, const char*);
 char *strtok(char*, const char*);
 size_t strxfrm(char*, const char*, size_t);
+char *strerror(int);
 
 #endif
diff --git a/kernel/fd.c b/kernel/fd.c
new file mode 100644
index 0000000..19068c4
--- /dev/null
+++ b/kernel/fd.c
@@ -0,0 +1,360 @@
+#include <asm/interrupt.h>
+#include <asm/io.h>
+#include <errno.h>
+#include <kernel/con.h>
+#include <kernel/fs.h>
+#include <kernel/kernel.h>
+#include <kernel/sched.h>
+#include <limits.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/types.h>
+
+#define FDBASE 0x3F0
+
+#define FDSRA   FDBASE
+#define FDSRB   (FDBASE + 1)
+#define FDDOR   (FDBASE + 2)
+#define FDTDR   (FDBASE + 3)
+#define FDMSR   (FDBASE + 4)
+#define FDDRS   (FDBASE + 4)
+#define FDDATA  (FDBASE + 5)
+#define FDDIR   (FDBASE + 7)
+#define FDCCR   (FDBASE + 7)
+
+#define SECTS(n) ((n) * (BLOCK_SIZE / 512))
+#define BLOCKS(n) ((n) / (BLOCK_SIZE / 512))
+
+#define NTYPES (sizeof(ftypes) / sizeof(struct ftype))
+#define NFDS (sizeof(fd) / sizeof(struct fdrive))
+
+/* helper macros for converting LBA into CHS */
+#define C(lba, ft) \
+  (lba / (ft->h * ft->s))
+#define H(lba, ft) \
+  ((lba / ft->s) % ft->h)
+#define S(lba, ft) \
+  ((lba % ft->s) + 1)
+
+#define PRESENT(fd) ((fd.type) && (fd.type != ftypes))
+
+/* TODO: replace any delay loops with sleep_on() */
+/* TODO: implement a head scheduling algorithm */
+/* TODO: implement write functionality */
+/* TODO: implement access to multiple drives */
+/* TODO: seek before reading */
+/* TODO: check drive ready state in floppy driver (ensure the drive door is closed before any operation) */
+/* TODO: cut back on printk() usage */
+
+/* TODO: implement a timeout to prevent system hangs */
+#define WAITIRQ(x) ({ \
+    irq_fired = 0; \
+    (x); \
+    while(!irq_fired); \
+    irq_fired = 0; \
+    })
+
+extern void fd_isr(void);
+
+struct sense_result {
+  uint8_t st0;
+  uint8_t cyl;
+} __attribute__((packed));
+
+struct ftype {
+  uint16_t c;
+  uint8_t h;
+  uint8_t s;
+  uint8_t drate; /* 0: 500Kb/s, 1: 300Kb/s, 2: 250Kb/s, 3: 1Mb/s */
+  int delay;     /* time to spin up (ms) */
+  char *name;
+};
+
+struct fdrive {
+  struct ftype *type;
+  struct task_struct *seek_wait;
+  uint8_t cyl;
+  uint8_t st0;
+};
+
+/* possible floppy disk/drive configurations */
+static struct ftype ftypes[] = {
+  {  0, 0,  0, 0,   0, "none" },
+  { 40, 2,  9, 1, 500, "360KB 5 1/4\"" },
+  { 80, 2, 15, 0, 500, "1.2MB 5 1/4\"" },
+  { 80, 2,  9, 2, 300, "720KB 3 1/2\"" },
+  { 80, 2, 18, 0, 300, "1.44MB 3 1/2\"" },
+  { 80, 2, 36, 3, 300, "2.88MB 3 1/2\"" }
+};
+
+static volatile int irq_fired;
+
+static struct fdrive fd[4];
+
+static char buffer[512] __attribute__((aligned (0x10000)));
+
+static struct task_struct *read_wait;
+
+static ssize_t read_data(void *buf, size_t len) {
+  ssize_t c = 0;
+  uint8_t *p = buf;
+
+  if(!buf)
+    return 0;
+
+  if(len > SSIZE_MAX)
+    len = SSIZE_MAX;
+
+  /*
+   * TODO: fix this.
+   * This entire routine really is garbage.
+   * It doesn't use a timeout (potentially
+   * hanging the entire system) and doesn't
+   * handle the DIO flag properly.
+   */
+  while(len--) {
+    while(!(inb(FDMSR) & 0x80));
+
+    if(!(inb(FDMSR) & 0x40))
+      break;
+
+    *p++ = inb(FDDATA);
+    c++;
+
+    /* delay */
+    inb(0x80);
+  }
+
+  /* empty out any remaining bytes the FDC may have for us */
+  while((inb(FDMSR) & 0xC0) == 0xC0)
+    inb(FDDATA);
+
+  if(!c)
+    return -1;
+  return c;
+}
+
+static void write_data(void *buf, size_t len) {
+  uint8_t *p = buf;
+
+  if(!buf)
+    return;
+
+  /* TODO: timeout waiting for RQM flag */
+  while(len--) {
+    while(!(inb(FDMSR) & 0x80));
+
+    if((inb(FDMSR) & 0x40)) {
+      printk("[fd] Expected DIO=0. Drive not ready for data!\n");
+      panic();
+    }
+
+    outb(FDDATA, *p++);
+
+    /* delay */
+    inb(0x80);
+  }
+}
+
+static int seek(uint8_t drive, int cyl) {
+  drive &= 3;
+
+  char cmd_seek[] = {
+    0x0F,
+    drive,
+    cyl
+  };
+
+  if(!PRESENT(fd[drive]))
+    return -EINVAL;
+
+  WAITIRQ(write_data(cmd_seek, sizeof(cmd_seek)));
+
+  /* wait for the seek command to finish */
+  while((inb(FDMSR) & (1 << drive)));
+
+  return 0;
+}
+
+static int sense_intr(struct sense_result *sr) {
+  ssize_t in;
+  char cmd_sense[] = { 0x08 };
+
+  /* send the sense interrupt command */
+  write_data(cmd_sense, sizeof(cmd_sense));
+  in = read_data(sr, sizeof(struct sense_result));
+  if(in < sizeof(struct sense_result))
+    return -1;
+
+  printk("[fd] Sense command success (Drive: %c:, CYL: 0x%02x, ST0: 0x%02x)\n", 'A' + (sr->st0 & 3), sr->cyl, sr->st0);
+  return 0;
+}
+
+static void reset(void) {
+  int i;
+  int wait = 0;
+  ssize_t in;
+  struct sense_result sr;
+
+  /* TODO: set timings depending on the drive */
+  char cmd_specify[] = {
+    0x03,
+    0xDF, /* SRT: 3ms, HUT: 240ms */
+    0x02  /* HLT: 16ms, NDMA: 0 */
+  };
+
+  char cmd_recalibrate[] = { 0x07, 0x00 };
+
+  /* disable interrupts and put the FDC into reset */
+  /* TODO: store FDDOR as static variable as the register is write-only */
+  printk("[fd] Resetting FDC...\n");
+  outb(FDDOR, inb(FDDOR) & 0xF3);
+
+  /* program the data-rate */
+  /* TODO: set this depending on floppy type */
+  outb(FDDRS, 0);
+  outb(FDCCR, 0);
+
+  /* bring the FDC out of reset and re-enable interrupts */
+  outb(FDDOR, inb(FDDOR) | 0x0C);
+
+  /* the IRQ handler will issue a sense-interrupt for us */
+  WAITIRQ(NULL);
+
+  /* send the specify command */
+  write_data(cmd_specify, sizeof(cmd_specify));
+
+  for(i = 0; i < NFDS; i++) {
+    if(!PRESENT(fd[i]))
+      continue;
+    printk("[fd] Recalibrating Drive %c:...\n", 'A' + i);
+    cmd_recalibrate[1] = i & 3;
+    write_data(cmd_recalibrate, sizeof(cmd_recalibrate));
+    wait |= 1 << i;
+  }
+
+  /* wait for all drives to finish recalibrating */
+  while((inb(FDMSR) & wait));
+}
+
+int fd_read_sect(int sect) {
+  ssize_t in;
+  struct {
+    uint8_t st0;
+    uint8_t st1;
+    uint8_t st2;
+    uint8_t c;
+    uint8_t h;
+    uint8_t r;
+    uint8_t n;
+  } __attribute__((packed)) res;
+
+  char cmd[] = {
+    0x46,
+    H(sect, fd[0].type) << 2,
+    C(sect, fd[0].type),
+    H(sect, fd[0].type),
+    S(sect, fd[0].type),
+    0x02,
+    S(sect, fd[0].type),
+    0x1B,
+    0xFF
+  };
+
+  cli();
+  if(read_wait)
+    sleep_on(&read_wait);
+  sti();
+
+  printk("[fd] Reading sector 0x%01x (C: 0x%01x, H: 0x%01x, S: 0x%01x)\n", sect, cmd[2], cmd[3], cmd[4]);
+
+  WAITIRQ(write_data(cmd, sizeof(cmd)));
+
+  in = read_data(&res, sizeof(res));
+  if(in == sizeof(res) && !(res.st0 & 0xC0)) {
+    printk("[fd] Successfully read a sector (ST0: 0x%02x, N: 0x%02x)!\n", res.st0, res.n);
+    printk("  DATA: %s\n", buffer);
+    return 0;
+  }
+
+  printk("[fd] Read command failed!\n");
+  return -1;
+}
+
+void fd_interrupt(void) {
+  struct sense_result sr;
+  irq_fired = 1;
+
+  wake_up(&read_wait);
+
+  if((inb(FDMSR) & 0xC0) != 0x80)
+    return;
+  if(sense_intr(&sr) < sizeof(sr))
+    return;
+  /* deposit result into current drive struct */
+  fd[sr.cyl & 3].cyl = sr.cyl;
+  fd[sr.st0 & 3].st0 = sr.st0;
+}
+
+void fd_block_read(struct buffer *b) {
+  int i;
+  void *p = b->b_data;
+
+  for(i = SECTS(b->b_block); i < SECTS(b->b_block + 1); i++) {
+    if(fd_read_sect(i)) {
+      b->b_device = 0;
+      return;
+    }
+    memcpy(p, buffer, sizeof(buffer));
+    p += 512;
+  }
+
+  b->b_present = 1;
+}
+
+void fd_init(void) {
+  int i;
+  int delay = 0;
+  uint8_t tmp;
+
+  /* put the controller into reset */
+  outb(FDDOR, 0);
+
+  outb(0x70, 0x10);
+  tmp = inb(0x71);
+
+  fd[0].type = &ftypes[(tmp >> 4) > NTYPES ? 0 : (tmp >> 4)];
+  fd[1].type = &ftypes[(tmp & 0xF) > NTYPES ? 0 : (tmp & 0xF)];
+  fd[2].type = ftypes;
+  fd[3].type = ftypes;
+
+  /* setup the drive (motors A and B on) */
+  /* TODO: motor timeout */
+  outb(FDDOR, 0x3C);
+
+  /* wait for all drives to spin up */
+  for(i = 0; i < NFDS; i++)
+    if(PRESENT(fd[i]))
+      delay = fd[i].type->delay > delay ? fd[i].type->delay : delay;
+  delay = (delay / 10) + ticks;
+  while(ticks < delay);
+
+  /* initialize the DMA controller */
+  outb(0x0F, 0x0F);
+  outb(0x0C, 0xFF);
+  outb(0x04, (uint32_t) buffer);
+  outb(0x04, (uint32_t) buffer >> 8);
+  outb(0x0C, 0xFF);
+  outb(0x05, sizeof(buffer));
+  outb(0x05, sizeof(buffer) >> 8);
+  outb(0x81, (uint32_t) buffer >> 16);
+  outb(0x0B, 0x56);
+  outb(0x0A, 0x02);
+
+  register_isr(0x26, 0, &fd_isr);
+  irq_enable(0x40);
+
+  reset();
+
+  printk("[fd] Floppy subsystem initialized (A: %s, B: %s)\n", fd[0].type->name, fd[1].type->name);
+}
diff --git a/kernel/fd_s.s b/kernel/fd_s.s
new file mode 100644
index 0000000..a8acb5b
--- /dev/null
+++ b/kernel/fd_s.s
@@ -0,0 +1,27 @@
+global fd_isr
+extern printk
+
+extern fd_interrupt
+
+fd_isr:
+  pusha
+  mov ax, ds
+  push ax
+  mov ax, 0x10
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+
+  call fd_interrupt
+
+  mov al, 0x20
+  out 0x20, al
+
+  pop ax
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+  popa
+  iret
diff --git a/kernel/fs/block.c b/kernel/fs/block.c
index caf97d2..8f9d907 100644
--- a/kernel/fs/block.c
+++ b/kernel/fs/block.c
@@ -1,9 +1,23 @@
+#include <kernel/fd.h>
+#include <kernel/fs.h>
 #include <sys/types.h>
 
-int block_read(void *buf, size_t block) {
-  return -1;
+/*
+ * Minix Major Numbers:
+ *
+ * [0] NULL
+ * [1] /dev/mem
+ * [2] /dev/fdX
+ * [3] /dev/hdX
+ * [4] /dev/ttyX
+ * [5] /dev/tty
+ * [6] /dev/lpX
+ */
+
+void block_read(struct buffer *b) {
+  fd_block_read(b);
 }
 
-int block_write(void *buf, size_t block) {
-  return -1;
+void block_write(struct buffer *b) {
+  b->b_device = 0;
 }
diff --git a/kernel/fs/buffer.c b/kernel/fs/buffer.c
index 7405738..99c3161 100644
--- a/kernel/fs/buffer.c
+++ b/kernel/fs/buffer.c
@@ -1,16 +1,76 @@
+#include <asm/interrupt.h>
+#include <errno.h>
 #include <kernel/con.h>
 #include <kernel/fs.h>
 #include <stdint.h>
 #include <string.h>
 
 /* memory dedicated to the block cache */
+/* TODO: start buffers at kernel end not 512K */
 #define BSTART 0x80000
 #define BEND 0xA0000
 
 static struct buffer *lru;
 static struct buffer *mru;
 
-struct buffer *buffer_get_block(uint16_t device, uint16_t block);
+struct buffer *buffer_get_block(uint16_t device, uint16_t block) {
+  struct buffer **p = &mru;
+  struct buffer *b;
+
+  if(!device)
+    return NULL;
+
+  /* check if the requested block is already in the cache */
+  while(b = *p) {
+    if(b->b_device != device || b->b_block != block)
+      goto next;
+    /* remove the buffer from the list */
+    if(lru == b && b->b_next)   lru = b->b_next;
+    if(b->b_next)               b->b_next->b_prev = b->b_prev;
+    if(b->b_prev)               b->b_prev->b_next = b->b_next;
+    /* put the buffer back at the MRU end of the list */
+    b->b_next = NULL;
+    b->b_prev = mru;
+    if(mru != b)
+      mru->b_next = b;
+    mru = b;
+    cli();
+    /* if the buffer exists but isn't populated. wait on it */
+    if(!b->b_present) {
+      sleep_on(&b->b_wait);
+      printk("[buf] Waiting for buffer %04x:%04x to be populated...\n", b->b_device, b->b_block);
+    }
+    sti();
+    printk("[buf] Fetched block %04x:%04x from cache\n", b->b_device, b->b_block);
+    return b->b_device ? b : NULL;
+next:
+    p = &b->b_prev;
+  }
+
+  /*
+   * otherwise, iterate through the least recently used
+   * buffers, to find a buffer that isn't pending an
+   * I/O operation, and read into it.
+   */
+
+  p = &lru;
+  while(b = *p) {
+    if(b->b_present || !b->b_device)
+      break;
+    p = &(*p)->b_next;
+  }
+
+  if(!b)
+    return NULL;
+
+  b->b_device = device;
+  b->b_block = block;
+  b->b_present = 0;
+  block_read(b);
+  wake_up(&b->b_wait);
+  printk("[buf] Called driver to read block %04x:%04x\n", b->b_device, b->b_block);
+  return b->b_device ? b : NULL;
+}
 
 void buffer_init(void) {
   int c = 0;
@@ -40,43 +100,3 @@ void buffer_init(void) {
 
   printk("[buf] Buffers initialized (0x%x buffers in pool)\n", c);
 }
-
-struct buffer *buffer_get_block(uint16_t device, uint16_t block) {
-  int ret;
-  struct buffer **p = &mru;
-  struct buffer *b;
-
-  /* check if the requested block is already in the cache */
-  while(*p) {
-    if((*p)->b_device == device && (*p)->b_block == block) {
-      /* put the buffer back at the MRU end of the list */
-      (*p)->b_next = NULL;
-      (*p)->b_prev = mru;
-      mru = *p;
-      return *p;
-    }
-    p = &(*p)->b_prev;
-  }
-
-  /* find a buffer at the end of the LRU list */
-  b = lru;
-  lru = lru->b_next;
-  lru->b_prev = NULL;
-  ret = block_read(b->b_data, block);
-  /* abort if we failed to read in the block */
-  if(ret < 0) {
-    /* release the allocated buffer to the pool */
-    lru->b_prev = b;
-    b->b_next = lru;
-    b->b_prev = NULL;
-    lru = b;
-    return NULL;
-  }
-  b->b_device = device;
-  b->b_block = block;
-  /* put the buffer back at the MRU end of the list */
-  b->b_next = NULL;
-  b->b_prev = mru;
-  mru = b;
-  return b;
-}
diff --git a/kernel/fs/fs.c b/kernel/fs/fs.c
index 381f20a..e460a4a 100644
--- a/kernel/fs/fs.c
+++ b/kernel/fs/fs.c
@@ -1,5 +1,6 @@
 #include <errno.h>
 #include <kernel/con.h>
+#include <kernel/fd.h>
 #include <kernel/fs.h>
 #include <kernel/kernel.h>
 #include <kernel/sched.h>
@@ -32,6 +33,7 @@ void fs_init(void) {
   buffer_init();
 
   /* hd_init(); */
+  fd_init();
 
   mount_root();
 }
diff --git a/kernel/fs/mount.c b/kernel/fs/mount.c
index 9cdf49b..e4d3636 100644
--- a/kernel/fs/mount.c
+++ b/kernel/fs/mount.c
@@ -7,15 +7,17 @@ struct super_block sblocks[NRSUPER];
 
 void mount_root(void) {
   int ret;
-  char buf[BLOCK_SIZE];
-  struct super_block *s = (void*) buf;
+  struct buffer *b;
+  struct super_block *s;
 
-  ret = block_read(buf, 1);
-  if(ret < 0) {
+  b = buffer_get_block(1, 1);
+  if(!b) {
     printk("[fs] Failed to read super block\n");
     return;
   }
 
+  s = b->b_data;
+
   if(s->s_magic != SUPER_MAGIC) {
     printk("[fs] Invalid magic number in super block!\n");
     return;
@@ -31,5 +33,5 @@ void mount_root(void) {
   printk("  Max file size: 0x%01x\n", s->s_max_size);
 
   /* copy the super block into the table */
-  memcpy(sblocks, buf, ((unsigned) &s->s_imap - (unsigned) s));
+  memcpy(sblocks, s, ((unsigned) &s->s_imap - (unsigned) s));
 }
diff --git a/kernel/hd.c b/kernel/hd.c
index 2f680d1..83108dd 100644
--- a/kernel/hd.c
+++ b/kernel/hd.c
@@ -40,7 +40,7 @@ static int read_sect(void *buf, uint32_t lba) {
   outb(0x1F7, 0x20);
 
   /* wait for the drive */
-  while(1) {
+  for(;;) {
     /* poll the drive's status */
     s = inb(0x1F7);
     if(s & ST_DF) {
@@ -81,7 +81,7 @@ static int write_sect(void *buf, uint32_t lba) {
   outb(0x1F7, 0x30);
 
   /* wait for the drive */
-  while(1) {
+  for(;;) {
     /* poll the drive's status */
     s = inb(0x1F7);
     if(s & ST_DF) {
@@ -102,15 +102,13 @@ static int write_sect(void *buf, uint32_t lba) {
   return 0;
 }
 
-int hd_read_block(void *buf, size_t block) {
+int hd_read_block(void *buf, uint16_t block) {
   int ret;
   size_t i;
   uint32_t s = SECTS(block);
   uint32_t e = SECTS(block + 1);
 
-  if(nblocks <= s)
-    return -1;
-  if(nblocks <= e)
+  if(nblocks <= s || nblocks <= e)
     return -1;
 
   for(i = 0; i < (e - s); i++) {
@@ -125,15 +123,13 @@ int hd_read_block(void *buf, size_t block) {
   return 0;
 }
 
-int hd_write_block(void *buf, size_t block) {
+int hd_write_block(void *buf, uint16_t block) {
   int ret;
   size_t i;
   uint32_t s = SECTS(block);
   uint32_t e = SECTS(block + 1);
 
-  if(nblocks <= s)
-    return -1;
-  if(nblocks <= e)
+  if(nblocks <= s || nblocks <= e)
     return -1;
 
   for(i = 0; i < (e - s); i++) {
@@ -158,7 +154,7 @@ int hd_init(void) {
   /* send the IDENTIFY command */
   outb(0x1F7, 0xEC);
 
-  while(1) {
+  for(;;) {
     s = inb(0x1F7);
     if(!s) {
       printk("[hd] Master drive not detected on primary bus!\n");
diff --git a/kernel/sched.c b/kernel/sched.c
index da55fa3..ff2d036 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -85,7 +85,8 @@ struct task_struct *create_proc(void *bin, size_t len) {
     }
   }
 
-  /* here we allocate pages to setup the process'
+  /*
+   * here we allocate pages to setup the process'
    * address space. in addition to the pages that
    * will hold the binary image, the following
    * pages are allocated:
@@ -222,7 +223,7 @@ void reschedule(void) {
     return;
 
   n = ctaskn;
-  while(1) {
+  for(;;) {
     /* check alarms and signals */
     for(i = 0; i < NRTASKS; i++) {
       if(tasks[i].alarm && tasks[i].alarm < ticks) {
@@ -288,7 +289,7 @@ void interruptible_sleep_on(struct task_struct **waiting) {
 
   t = *waiting;
   *waiting = ctask;
-  while(1) {
+  for(;;) {
     ctask->state = TSTATE_INTERRUPTIBLE;
     reschedule();
 
diff --git a/kernel/tty.c b/kernel/tty.c
index 529d955..a17429f 100644
--- a/kernel/tty.c
+++ b/kernel/tty.c
@@ -20,7 +20,7 @@ static struct tty_struct *ttys[] = {
 /* check if a buffer's empty and if so, go to sleep */
 static int sleep_while_empty(struct tty_queue *q) {
   cli();
-  while(1) {
+  for(;;) {
     if(q->pread == q->pwrite)
       interruptible_sleep_on(&q->waiting);
 
@@ -38,7 +38,7 @@ static int sleep_while_empty(struct tty_queue *q) {
 /* check if a buffer's full and if so, go to sleep */
 static int sleep_while_full(struct tty_queue *q, struct tty_struct *tty) {
   cli();
-  while(1) {
+  for(;;) {
     /*
      * if the buffer is full, first notify the
      * driver so it can try to remove some
diff --git a/lib/string.c b/lib/string.c
index e8659ad..99ffdf0 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -1,5 +1,144 @@
+#include <errno.h>
 #include <string.h>
 
+static char *errors[] = {
+  [0]                =  "Success",
+  [EPERM]            =  "Operation not permitted",
+  [ENOENT]           =  "No such file or directory",
+  [ESRCH]            =  "No such process",
+  [EINTR]            =  "Interrupted system call",
+  [EIO]              =  "Input/output error",
+  [ENXIO]            =  "No such device or address",
+  [E2BIG]            =  "Argument list too long",
+  [ENOEXEC]          =  "Exec format error",
+  [EBADF]            =  "Bad file descriptor",
+  [ECHILD]           =  "No child processes",
+  [EAGAIN]           =  "Resource temporarily unavailable",
+  [EWOULDBLOCK]      =  "Resource temporarily unavailable",
+  [ENOMEM]           =  "Cannot allocate memory",
+  [EACCES]           =  "Permission denied",
+  [EFAULT]           =  "Bad address",
+  [ENOTBLK]          =  "Block device required",
+  [EBUSY]            =  "Device or resource busy",
+  [EEXIST]           =  "File exists",
+  [EXDEV]            =  "Invalid cross-device link",
+  [ENODEV]           =  "No such device",
+  [ENOTDIR]          =  "Not a directory",
+  [EISDIR]           =  "Is a directory",
+  [EINVAL]           =  "Invalid argument",
+  [ENFILE]           =  "Too many open files in system",
+  [EMFILE]           =  "Too many open files",
+  [ENOTTY]           =  "Inappropriate ioctl for device",
+  [ETXTBSY]          =  "Text file busy",
+  [EFBIG]            =  "File too large",
+  [ENOSPC]           =  "No space left on device",
+  [ESPIPE]           =  "Illegal seek",
+  [EROFS]            =  "Read-only file system",
+  [EMLINK]           =  "Too many links",
+  [EPIPE]            =  "Broken pipe",
+  [EDOM]             =  "Numerical argument out of domain",
+  [ERANGE]           =  "Numerical result out of range",
+  [EDEADLK]          =  "Resource deadlock avoided",
+  [EDEADLOCK]        =  "Resource deadlock avoided",
+  [ENAMETOOLONG]     =  "File name too long",
+  [ENOLCK]           =  "No locks available",
+  [ENOSYS]           =  "Function not implemented",
+  [ENOTEMPTY]        =  "Directory not empty",
+  [ELOOP]            =  "Too many levels of symbolic links",
+  [ENOMSG]           =  "No message of desired type",
+  [EIDRM]            =  "Identifier removed",
+  [ECHRNG]           =  "Channel number out of range",
+  [EL2NSYNC]         =  "Level 2 not synchronized",
+  [EL3HLT]           =  "Level 3 halted",
+  [EL3RST]           =  "Level 3 reset",
+  [ELNRNG]           =  "Link number out of range",
+  [EUNATCH]          =  "Protocol driver not attached",
+  [ENOCSI]           =  "No CSI structure available",
+  [EL2HLT]           =  "Level 2 halted",
+  [EBADE]            =  "Invalid exchange",
+  [EBADR]            =  "Invalid request descriptor",
+  [EXFULL]           =  "Exchange full",
+  [ENOANO]           =  "No anode",
+  [EBADRQC]          =  "Invalid request code",
+  [EBADSLT]          =  "Invalid slot",
+  [EBFONT]           =  "Bad font file format",
+  [ENOSTR]           =  "Device not a stream",
+  [ENODATA]          =  "No data available",
+  [ETIME]            =  "Timer expired",
+  [ENOSR]            =  "Out of streams resources",
+  [ENONET]           =  "Machine is not on the network",
+  [ENOPKG]           =  "Package not installed",
+  [EREMOTE]          =  "Object is remote",
+  [ENOLINK]          =  "Link has been severed",
+  [EADV]             =  "Advertise error",
+  [ESRMNT]           =  "Srmount error",
+  [ECOMM]            =  "Communication error on send",
+  [EPROTO]           =  "Protocol error",
+  [EMULTIHOP]        =  "Multihop attempted",
+  [EDOTDOT]          =  "RFS specific error",
+  [EBADMSG]          =  "Bad message",
+  [EOVERFLOW]        =  "Value too large for defined data type",
+  [ENOTUNIQ]         =  "Name not unique on network",
+  [EBADFD]           =  "File descriptor in bad state",
+  [EREMCHG]          =  "Remote address changed",
+  [ELIBACC]          =  "Can not access a needed shared library",
+  [ELIBBAD]          =  "Accessing a corrupted shared library",
+  [ELIBSCN]          =  ".lib section in a.out corrupted",
+  [ELIBMAX]          =  "Attempting to link in too many shared libraries",
+  [ELIBEXEC]         =  "Cannot exec a shared library directly",
+  [EILSEQ]           =  "Invalid or incomplete multibyte or wide character",
+  [ERESTART]         =  "Interrupted system call should be restarted",
+  [ESTRPIPE]         =  "Streams pipe error",
+  [EUSERS]           =  "Too many users",
+  [ENOTSOCK]         =  "Socket operation on non-socket",
+  [EDESTADDRREQ]     =  "Destination address required",
+  [EMSGSIZE]         =  "Message too long",
+  [EPROTOTYPE]       =  "Protocol wrong type for socket",
+  [ENOPROTOOPT]      =  "Protocol not available",
+  [EPROTONOSUPPORT]  =  "Protocol not supported",
+  [ESOCKTNOSUPPORT]  =  "Socket type not supported",
+  [ENOTSUP]          =  "Operation not supported",
+  [EOPNOTSUPP]       =  "Operation not supported",
+  [EPFNOSUPPORT]     =  "Protocol family not supported",
+  [EAFNOSUPPORT]     =  "Address family not supported by protocol",
+  [EADDRINUSE]       =  "Address already in use",
+  [EADDRNOTAVAIL]    =  "Cannot assign requested address",
+  [ENETDOWN]         =  "Network is down",
+  [ENETUNREACH]      =  "Network is unreachable",
+  [ENETRESET]        =  "Network dropped connection on reset",
+  [ECONNABORTED]     =  "Software caused connection abort",
+  [ECONNRESET]       =  "Connection reset by peer",
+  [ENOBUFS]          =  "No buffer space available",
+  [EISCONN]          =  "Transport endpoint is already connected",
+  [ENOTCONN]         =  "Transport endpoint is not connected",
+  [ESHUTDOWN]        =  "Cannot send after transport endpoint shutdown",
+  [ETOOMANYREFS]     =  "Too many references: cannot splice",
+  [ETIMEDOUT]        =  "Connection timed out",
+  [ECONNREFUSED]     =  "Connection refused",
+  [EHOSTDOWN]        =  "Host is down",
+  [EHOSTUNREACH]     =  "No route to host",
+  [EALREADY]         =  "Operation already in progress",
+  [EINPROGRESS]      =  "Operation now in progress",
+  [ESTALE]           =  "Stale file handle",
+  [EUCLEAN]          =  "Structure needs cleaning",
+  [ENOTNAM]          =  "Not a XENIX named type file",
+  [ENAVAIL]          =  "No XENIX semaphores available",
+  [EISNAM]           =  "Is a named type file",
+  [EREMOTEIO]        =  "Remote I/O error",
+  [EDQUOT]           =  "Disk quota exceeded",
+  [ENOMEDIUM]        =  "No medium found",
+  [EMEDIUMTYPE]      =  "Wrong medium type",
+  [ECANCELED]        =  "Operation canceled",
+  [ENOKEY]           =  "Required key not available",
+  [EKEYEXPIRED]      =  "Key has expired",
+  [EKEYREVOKED]      =  "Key has been revoked",
+  [EKEYREJECTED]     =  "Key was rejected by service",
+  [EOWNERDEAD]       =  "Owner died",
+  [ENOTRECOVERABLE]  =  "State not recoverable",
+  [ERFKILL]          =  "Operation not possible due to RF-kill",
+  [EHWPOISON]        =  "Memory page has hardware error",
+};
+
 void *memchr(const void *s, int c, size_t n) {
   unsigned char *p = (unsigned char*) s;
   while(n--) {
@@ -171,3 +310,12 @@ size_t strxfrm(char *dest, const char *src, size_t n) {
   if(n > n2) strcpy(dest, src);
   return n2;
 }
+
+char *strerror(int err) {
+  err = err < 0 ? -err : err;
+
+  if(err > sizeof(errors) / sizeof(char*))
+    return NULL;
+
+  return errors[err];
+}
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index a566b83..4188308 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -6,8 +6,9 @@ enum TYPE {
   TYPE_INT      = 1,
   TYPE_UINT     = 2,
   TYPE_HEX      = 3,
-  TYPE_STRING   = 4,
-  TYPE_PERCENT  = 5
+  TYPE_CHAR     = 4,
+  TYPE_STRING   = 5,
+  TYPE_PERCENT  = 6
 };
 
 enum FLAGS {
@@ -91,7 +92,7 @@ int vsprintf(char *str, char *fmt, va_list ap) {
     fwidth = 0;
 
     fmt++;
-    while(1) {
+    for(;;) {
       switch(*fmt) {
         case '#':
           flags |= FL_ALT;
@@ -99,6 +100,9 @@ int vsprintf(char *str, char *fmt, va_list ap) {
         case '%':
           type = TYPE_PERCENT;
           goto done;
+        case 'c':
+          type = TYPE_CHAR;
+          goto done;
         case 's':
           type = TYPE_STRING;
           goto done;
@@ -137,6 +141,9 @@ done:
         while(*s)
           *str++ = *s++;
         break;
+      case TYPE_CHAR:
+        *str++ = va_arg(ap, char);
+        break;
       case TYPE_HEX:
         x = va_arg(ap, int);
         hex(&str, flags, fwidth, 4, x);
diff --git a/usrbin/main.c b/usrbin/main.c
index c4a257c..f05cb84 100644
--- a/usrbin/main.c
+++ b/usrbin/main.c
@@ -1,7 +1,9 @@
 #include <errno.h>
+#include <kernel/fs.h>
 #include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -16,7 +18,7 @@ void pid1(void) {
   printf("We did it ma!\n");
   signal(1, &sighandler);
 
-  while(1) {
+  for(;;) {
     in = read(STDIN_FILENO, buf, 1);
     if(in < 1) {
       if(in == -EINTR) {
@@ -41,7 +43,7 @@ void pid2(void) {
 
   printf("We did it ma!\n");
 
-  while(1) {
+  for(;;) {
     sleep(1);
     if(time() == 2)
       kill(1, 1);