From fb34b20ce0920edf1b34d9f23ecf768d1a66645f Mon Sep 17 00:00:00 2001
From: Francesco Lavra <francescolavra@nanovms.com>
Date: Sun, 24 May 2026 19:46:30 +0200
Subject: [PATCH 1/2] file_open(): Refactor to avoid multiple table lookups

The is_dir() call is somewhat expensive, as is does a table lookup, and
file_open() contains a couple of these function calls; then, there is a
file_type_from_tuple() call which can potentially re-do the same lookups
again.
To avoid multiple table lookups, move the file_type_from_tuple() call at
the top of the function, so that the `type` variable can be compared
against known values in the rest of the function.
No functional changes.
---
 src/unix/syscall.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/unix/syscall.c b/src/unix/syscall.c
index 0bf93c1fe..038f3a6f0 100755
--- a/src/unix/syscall.c
+++ b/src/unix/syscall.c
@@ -842,6 +842,7 @@ int file_open(filesystem fs, tuple n, tuple parent, int flags, fsfile fsf)
 {
     thread t = current;
     process p = t->p;
+    int type = file_type_from_tuple(n);
 
     if (flags & O_TMPFILE)
         flags |= O_DIRECTORY;
@@ -860,26 +861,23 @@ int file_open(filesystem fs, tuple n, tuple parent, int flags, fsfile fsf)
         if (!(file_meta_perms(p, n) & ACCESS_PERM_WRITE)) {
             return -EACCES;
         }
-        if (is_dir(n) && !(flags & O_TMPFILE)) {
+        if ((type == FDESC_TYPE_DIRECTORY) && !(flags & O_TMPFILE)) {
             return -EISDIR;
         }
         break;
     default:
         return -EINVAL;
     }
-    if ((flags & (O_CREAT|O_DIRECTORY)) == O_DIRECTORY && !is_dir(n)) {
+    if ((flags & (O_CREAT|O_DIRECTORY)) == O_DIRECTORY && (type != FDESC_TYPE_DIRECTORY)) {
         return -ENOTDIR;
     }
 
-    int type;
-
     if (flags & O_TMPFILE) {
         int fss = filesystem_creat_unnamed(fs, &fsf);
         if (fss != 0)
             return fss;
         type = FDESC_TYPE_REGULAR;
     } else {
-        type = file_type_from_tuple(n);
         if (type == FDESC_TYPE_REGULAR) {
             assert(fsf);
             if (flags & O_TRUNC)

From e6579d21c64e0678874e7ef314de867ec1715d8f Mon Sep 17 00:00:00 2001
From: Francesco Lavra <francescolavra@nanovms.com>
Date: Sun, 24 May 2026 19:52:36 +0200
Subject: [PATCH 2/2] file_open: Do not return -EROFS when opening non-regular
 files

open() with O_WRONLY or O_RDWR on device files like /dev/null returns EROFS
when the `readonly_rootfs` manifest option is enabled. Writes to
non-regular files do not modify the filesystem, so these files should be
exempt from the read-only check.
---
 src/unix/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/unix/syscall.c b/src/unix/syscall.c
index 038f3a6f0..68a100601 100755
--- a/src/unix/syscall.c
+++ b/src/unix/syscall.c
@@ -855,7 +855,7 @@ int file_open(filesystem fs, tuple n, tuple parent, int flags, fsfile fsf)
         break;
     case O_WRONLY:
     case O_RDWR:
-        if (filesystem_is_readonly(fs)) {
+        if ((type == FDESC_TYPE_REGULAR) && filesystem_is_readonly(fs)) {
             return -EROFS;
         }
         if (!(file_meta_perms(p, n) & ACCESS_PERM_WRITE)) {