From 751b50a72412fbf385c4398f2cd62e22c33056ac Mon Sep 17 00:00:00 2001
From: Rick Gaiser <rgaiser@gmail.com>
Date: Sun, 1 Nov 2026 10:05:19 +0100
Subject: [PATCH] ps2client: open host: files read-write as O_RDWR

The PS2's open flags hold the access mode in the low two bits (1 read,
2 write, 3 both). fix_flags or-ed O_RDONLY and O_WRONLY for 3, which is
O_WRONLY | O_TRUNC on POSIX hosts: a file opened read-write was emptied
and every read of it returned 0 bytes. Map the mode as a whole; 3 is now
O_RDWR (without O_TRUNC).

tests: the fake's rdwrback reads a file opened with flags 3; its size and
CRC must match.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/utility.c        | 11 ++++++++---
 tests/fake_ps2link.c | 15 +++++++++------
 tests/run-tests.sh   |  6 ++++++
 3 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/src/utility.c b/src/utility.c
index d3ac43d..90a2d1e 100644
--- a/src/utility.c
+++ b/src/utility.c
@@ -17,9 +17,14 @@
 
  int fix_flags(int flags) { int result = 0;
 
-  // Fix the flags.
-  if (flags & 0x0001) { result |= O_RDONLY;           }
-  if (flags & 0x0002) { result |= O_WRONLY | O_TRUNC; } // FIXME: Truncate is needed for some programs.
+  // Fix the flags: the access mode is the low two bits (1 read, 2 write,
+  // 3 both). Read and write is O_RDWR, not O_RDONLY | O_WRONLY (which is
+  // O_WRONLY on most hosts, so reads fail).
+  switch (flags & 0x0003) {
+   case 0x0001: result |= O_RDONLY;           break;
+   case 0x0002: result |= O_WRONLY | O_TRUNC; break; // FIXME: Truncate is needed for some programs.
+   case 0x0003: result |= O_RDWR;             break;
+  }
 #ifndef _WIN32
   if (flags & 0x0010) { result |= O_NONBLOCK;         }
 #endif
diff --git a/tests/fake_ps2link.c b/tests/fake_ps2link.c
index 1e75b9d..d0239f9 100644
--- a/tests/fake_ps2link.c
+++ b/tests/fake_ps2link.c
@@ -129,12 +129,12 @@ static int fake_write(int fd, const unsigned char *data, int length)
     pthread_mutex_unlock(&fake.lock);
     return result;
 }
-static unsigned char *load_file(const char *path, size_t *length)
+static unsigned char *load_file(const char *path, int flags, size_t *length)
 {
     unsigned char *data = NULL;
     unsigned char chunk[128 * 1024];
     size_t allocated = 0;
-    int fd = fake_open(path, 1), n;
+    int fd = fake_open(path, flags), n;
     *length = 0;
     if (fd < 0) return NULL;
     while ((n = fake_read(fd, chunk, sizeof(chunk))) > 0) {
@@ -217,12 +217,15 @@ static void *run_script(void *context)
             }
             pthread_mutex_unlock(&fake.lock);
             break;
-        } else if (!strcmp(line, "readback")) {
+        } else if (!strcmp(line, "readback") || !strcmp(line, "rdwrback")) {
+            /* rdwrback: the same, the file opened for reading and writing
+             * (PS2 flags 3) */
+            int rdwr = !strcmp(line, "rdwrback");
             size_t length = 0;
-            unsigned char *data = load_file(arg, &length);
+            unsigned char *data = load_file(arg, rdwr ? 3 : 1, &length);
             if (data) {
                 char report[128];
-                snprintf(report, sizeof(report), "readback %zu %08x",
+                snprintf(report, sizeof(report), "%s %zu %08x", line,
                          length, crc32_bytes(data, length));
                 line_out(report);
                 free(data);
@@ -261,7 +264,7 @@ static void command_packet(unsigned char *packet, size_t length)
         args[255] = '\0';
         first = args;
         path = strncmp(first, "host:", 5) == 0 ? first + 5 : first;
-        script = load_file(path, &size);
+        script = load_file(path, 1, &size);
         if (!script) { line_out("fake: could not load script"); return; }
         offset = strnlen(first, sizeof(args)) + 1;
         for (i = 1; i < count && offset < 256; i++) {
diff --git a/tests/run-tests.sh b/tests/run-tests.sh
index cb85925..643c3a8 100755
--- a/tests/run-tests.sh
+++ b/tests/run-tests.sh
@@ -143,6 +143,12 @@ printf 'readback blob.bin\nprint @@END@@ status=0\n' > readback.elf
 check "big host: read" 0 "${H[@]}" -t 10 -e @@END@@ execee host:readback.elf
 expect "readback size and crc" grep -q "^readback 300000 $("$HERE/../bin/crc32" blob.bin)$" out.txt
 
+# --- a host: file opened for reading and writing (PS2 flags 3) can be read,
+# and is not truncated
+printf 'rdwrback blob.bin\nprint @@END@@ status=0\n' > rdwr.elf
+check "host: read of a read-write file" 0 "${H[@]}" -t 10 -e @@END@@ execee host:rdwr.elf
+expect "read-write: size and crc" grep -q "^rdwrback 300000 $("$HERE/../bin/crc32" blob.bin)$" out.txt
+
 # --- second client
 "$CLIENT" "${H[@]}" -t 5 listen > /dev/null 2>&1 &
 LISTENER=$!