sb: Allow input to be "ignored"

This removes edge cases from read calls and makes bugs harder
to introduce.

4 files changed, 42 insertions, 15 deletions

diff --git a/kernel/fs/procfs.c b/kernel/fs/procfs.c
index 69022d4..bfe3aac 100644
--- a/kernel/fs/procfs.c
+++ b/kernel/fs/procfs.c
@@ -23,8 +23,7 @@ void process_close(vfs_fd_t *fd) {
 int procfs_read(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
   struct sb builder;
   sb_init_buffer(&builder, buffer, len);
-
-  size_t read_amount = 0;
+  sb_set_ignore(&builder, offset);
 
   process_t *p = ready_queue;
   for (; p; p = p->next) {
@@ -32,13 +31,11 @@ int procfs_read(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
     entry.d_ino = p->pid;
     ksnprintf(entry.d_name, sizeof(entry.d_name), "%u", p->pid);
 
-    if (read_amount >= offset) {
-      if (0 == sb_append_buffer(&builder, (u8 *)&entry, sizeof(entry))) {
-        break;
-      }
+    if (0 == sb_append_buffer(&builder, (u8 *)&entry, sizeof(entry))) {
+      break;
     }
-    read_amount += sizeof(struct dirent);
   }
+
   return sv_length(SB_TO_SV(builder));
 }
 
@@ -70,27 +67,23 @@ int process_read(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
 
   struct sb builder;
   sb_init_buffer(&builder, buffer, len);
+  sb_set_ignore(&builder, offset);
 
   int id = fd->inode->inode_num;
   if (PROCESS_ROOT == id) {
-    size_t read_amount = 0;
     for (size_t i = 0; i < ARRAY_LENGTH(process_entries); i++) {
       if (0 == strlen(process_entries[i].d_name)) {
         continue;
       }
-      if (read_amount >= offset) {
-        if (0 == sb_append_buffer(&builder, (u8 *)&process_entries[i],
-                                  sizeof(struct dirent))) {
-          break;
-        }
+      if (0 == sb_append_buffer(&builder, (u8 *)&process_entries[i],
+                                sizeof(struct dirent))) {
+        break;
       }
-      read_amount += sizeof(struct dirent);
     }
     return sv_length(SB_TO_SV(builder));
   }
   if (PROCESS_NAME == id) {
     struct sv program_name = C_TO_SV(p->program_name);
-    sv_take(program_name, &program_name, offset);
     sb_append_sv(&builder, program_name);
     return sv_length(SB_TO_SV(builder));
   }
diff --git a/kernel/lib/sb.c b/kernel/lib/sb.c
index 6f716ac..ca302f7 100644
--- a/kernel/lib/sb.c
+++ b/kernel/lib/sb.c
@@ -11,6 +11,7 @@ void sb_init(struct sb *ctx) {
 }
 
 int sb_init_capacity(struct sb *ctx, size_t starting_capacity) {
+  ctx->to_ignore = 0;
   ctx->length = 0;
   ctx->prebuffer = 0;
   ctx->string = kmalloc(starting_capacity);
@@ -27,6 +28,7 @@ void sb_init_buffer(struct sb *ctx, char *buffer, size_t size) {
   ctx->capacity = size;
   ctx->length = 0;
   ctx->prebuffer = 1;
+  ctx->to_ignore = 0;
 }
 
 void sb_free(struct sb *ctx) {
@@ -40,8 +42,13 @@ void sb_free(struct sb *ctx) {
   ctx->string = NULL;
 }
 
+void sb_set_ignore(struct sb *ctx, size_t n) {
+  ctx->to_ignore = n;
+}
+
 void sb_reset(struct sb *ctx) {
   ctx->length = 0;
+  ctx->to_ignore = 0;
 }
 
 int sb_isempty(const struct sb *ctx) {
@@ -64,6 +71,10 @@ int sb_increase_buffer(struct sb *ctx, size_t min) {
 }
 
 int sb_append_char(struct sb *ctx, char c) {
+  if (ctx->to_ignore > 0) {
+    ctx->to_ignore--;
+    return 1;
+  }
   if (1 > ctx->capacity - ctx->length) {
     if (!sb_increase_buffer(ctx, 1)) {
       return 0;
@@ -82,6 +93,13 @@ int sb_delete_right(struct sb *ctx, size_t n) {
 
 int sb_append(struct sb *ctx, const char *s) {
   size_t l = strlen(s);
+  if (ctx->to_ignore >= l) {
+    ctx->to_ignore -= l;
+    return 1;
+  }
+  l -= ctx->to_ignore;
+  s += ctx->to_ignore;
+  ctx->to_ignore = 0;
   if (l > ctx->capacity - ctx->length) {
     if (!sb_increase_buffer(ctx, l)) {
       return 0;
@@ -97,6 +115,13 @@ int sb_prepend_sv(struct sb *ctx, struct sv sv) {
 }
 
 int sb_prepend_buffer(struct sb *ctx, const char *buffer, size_t length) {
+  if (ctx->to_ignore >= length) {
+    ctx->to_ignore -= length;
+    return 1;
+  }
+  length -= ctx->to_ignore;
+  buffer += ctx->to_ignore;
+  ctx->to_ignore = 0;
   if (length > ctx->capacity - ctx->length) {
     if (!sb_increase_buffer(ctx, length)) {
       return 0;
@@ -109,6 +134,13 @@ int sb_prepend_buffer(struct sb *ctx, const char *buffer, size_t length) {
 }
 
 int sb_append_buffer(struct sb *ctx, const char *buffer, size_t length) {
+  if (ctx->to_ignore >= length) {
+    ctx->to_ignore -= length;
+    return 1;
+  }
+  length -= ctx->to_ignore;
+  buffer += ctx->to_ignore;
+  ctx->to_ignore = 0;
   if (length > ctx->capacity - ctx->length) {
     if (!sb_increase_buffer(ctx, length)) {
       return 0;
diff --git a/kernel/lib/sb.h b/kernel/lib/sb.h
index 7832015..4d910e3 100644
--- a/kernel/lib/sb.h
+++ b/kernel/lib/sb.h
@@ -8,12 +8,14 @@ struct sb {
   char *string;
   size_t length;
   size_t capacity;
+  size_t to_ignore;
   uint8_t prebuffer;
 };
 
 struct sv;
 
 void sb_init(struct sb *ctx);
+void sb_set_ignore(struct sb *ctx, size_t n);
 int sb_init_capacity(struct sb *ctx, size_t starting_capacity);
 void sb_init_buffer(struct sb *ctx, char *buffer, size_t size);
 void sb_free(struct sb *ctx);
diff --git a/userland/libc/crt0.s b/userland/libc/crt1.s
index c950949..c950949 100644
--- a/userland/libc/crt0.s
+++ b/userland/libc/crt1.s