From 1b8b113536b560039ac02f224ce02315d9fb0fe5 Mon Sep 17 00:00:00 2001
From: James Stanley <james@incoherency.co.uk>
Date: Wed, 16 Oct 2019 19:55:12 +0100
Subject: [PATCH] Fix filesystem in shell emulator

We now treat the block device as fixed-size rather than trying to grow it in response
to kernel activity.

Previously, if you tried to create 2 files in a row, only the first 1 would actually appear,
because the device only ever got larger when a byte was written immediately past the end of
the device.

Now we just let the kernel write bytes to the disk anywhere, so new files can be created even
when the previous file is not completely full.

Also, fix buffer overrun in reading filesystem image, and use a more idiomatic fgetc loop.
---
 tools/emul/shell/shell.c | 36 ++++++++++++------------------------
 1 file changed, 12 insertions(+), 24 deletions(-)

diff --git a/tools/emul/shell/shell.c b/tools/emul/shell/shell.c
index 4dc4717..d24e565 100644
--- a/tools/emul/shell/shell.c
+++ b/tools/emul/shell/shell.c
@@ -41,7 +41,6 @@
 #define FS_ADDR_PORT 0x02
 
 static uint8_t fsdev[MAX_FSDEV_SIZE] = {0};
-static uint32_t fsdev_size = 0;
 static uint32_t fsdev_ptr = 0;
 // 0 = idle, 1 = received MSB (of 24bit addr), 2 = received middle addr
 static int  fsdev_addr_lvl = 0;
@@ -62,16 +61,13 @@ static uint8_t iord_fsdata()
         fprintf(stderr, "Reading FSDEV in the middle of an addr op (%d)\n", fsdev_ptr);
         return 0;
     }
-    if (fsdev_ptr < fsdev_size) {
+    if (fsdev_ptr < MAX_FSDEV_SIZE) {
 #ifdef DEBUG
         fprintf(stderr, "Reading FSDEV at offset %d\n", fsdev_ptr);
 #endif
         return fsdev[fsdev_ptr];
     } else {
-        // don't warn when ==, we're not out of bounds, just at the edge.
-        if (fsdev_ptr > fsdev_size) {
-            fprintf(stderr, "Out of bounds FSDEV read at %d\n", fsdev_ptr);
-        }
+        fprintf(stderr, "Out of bounds FSDEV read at %d\n", fsdev_ptr);
         return 0;
     }
 }
@@ -80,11 +76,9 @@ static uint8_t iord_fsaddr()
 {
     if (fsdev_addr_lvl != 0) {
         return 3;
-    } else if (fsdev_ptr > fsdev_size) {
-        fprintf(stderr, "Out of bounds FSDEV addr request at %d / %d\n", fsdev_ptr, fsdev_size);
+    } else if (fsdev_ptr >= MAX_FSDEV_SIZE) {
+        fprintf(stderr, "Out of bounds FSDEV addr request at %d / %d\n", fsdev_ptr, MAX_FSDEV_SIZE);
         return 2;
-    } else if (fsdev_ptr == fsdev_size) {
-        return 1;
     } else {
         return 0;
     }
@@ -105,18 +99,11 @@ static void iowr_fsdata(uint8_t val)
         fprintf(stderr, "Writing to FSDEV in the middle of an addr op (%d)\n", fsdev_ptr);
         return;
     }
-    if (fsdev_ptr < fsdev_size) {
+    if (fsdev_ptr < MAX_FSDEV_SIZE) {
 #ifdef DEBUG
         fprintf(stderr, "Writing to FSDEV (%d)\n", fsdev_ptr);
 #endif
         fsdev[fsdev_ptr] = val;
-    } else if ((fsdev_ptr == fsdev_size) && (fsdev_ptr < MAX_FSDEV_SIZE)) {
-        // We're at the end of fsdev, grow it
-        fsdev[fsdev_ptr] = val;
-        fsdev_size++;
-#ifdef DEBUG
-        fprintf(stderr, "Growing FSDEV (%d)\n", fsdev_ptr);
-#endif
     } else {
         fprintf(stderr, "Out of bounds FSDEV write at %d\n", fsdev_ptr);
     }
@@ -167,13 +154,14 @@ int main(int argc, char *argv[])
     if (fp != NULL) {
         fprintf(stderr, "Initializing filesystem\n");
         int i = 0;
-        int c = fgetc(fp);
-        while (c != EOF) {
-            fsdev[i] = c & 0xff;
-            i++;
-            c = fgetc(fp);
+        int c;
+        while ((c = fgetc(fp)) != EOF && i < MAX_FSDEV_SIZE) {
+            fsdev[i++] = c & 0xff;
+        }
+        if (i == MAX_FSDEV_SIZE) {
+            fprintf(stderr, "Filesytem image too large.\n");
+            return 1;
         }
-        fsdev_size = i;
         pclose(fp);
     }