[Qemu-devel] [PATCH 2/2] hw/9pfs: Read-only support for 9p export

["M. Mohan Kumar" <mohan@in.ibm.com>]

From: "M. Mohan Kumar" <mohan@in.ibm.com>

A new fsdev parameter "readonly" is introduced to control accessing 9p export.
readonly=on|off can be used to specify the access type. By default rw access
is given to 9p export.

Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>

---
Changes from previous version V4:
* Updated on top of current for-upstream branch

Changes from previous version V3:
* Use opt_set_bool function to set readonly option
* Change the flag from MS_READONLY to 9p specific

Change from previous version V2:
* QEMU_OPT_BOOL is used for readdonly parameter

Changes from previous version:
* Use "readonly" option instead of "access"
* Change function return type to boolean where its needed

 fsdev/file-op-9p.h  |    2 ++
 fsdev/qemu-fsdev.c  |    7 ++++++-
 hw/9pfs/virtio-9p.c |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 qemu-config.c       |    7 +++++++
 vl.c                |    2 ++
 5 files changed, 68 insertions(+), 1 deletions(-)

diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h
index c7b4e38..ba564d4 100644
--- a/fsdev/file-op-9p.h
+++ b/fsdev/file-op-9p.h
@@ -60,6 +60,8 @@ typedef struct extended_ops {
 
 #define V9FS_SEC_MASK               0x0000001C
 
+#define V9FS_RDONLY                 0x00000020
+
 typedef struct FsContext
 {
     uid_t uid;
diff --git a/fsdev/qemu-fsdev.c b/fsdev/qemu-fsdev.c
index e8dc0fd..7fd2aa7 100644
--- a/fsdev/qemu-fsdev.c
+++ b/fsdev/qemu-fsdev.c
@@ -36,7 +36,7 @@ int qemu_fsdev_add(QemuOpts *opts)
     const char *path = qemu_opt_get(opts, "path");
     const char *sec_model = qemu_opt_get(opts, "security_model");
     const char *writeout = qemu_opt_get(opts, "writeout");
-
+    bool ro = qemu_opt_get_bool(opts, "readonly", 0);
 
     if (!fsdev_id) {
         fprintf(stderr, "fsdev: No id specified\n");
@@ -87,6 +87,11 @@ int qemu_fsdev_add(QemuOpts *opts)
             fsle->fse.export_flags |= V9FS_IMMEDIATE_WRITEOUT;
         }
     }
+    if (ro) {
+        fsle->fse.export_flags |= V9FS_RDONLY;
+    } else {
+        fsle->fse.export_flags &= ~V9FS_RDONLY;
+    }
 
     if (strcmp(fsdriver, "local")) {
         goto done;
diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index 1c67bfe..b6770e2 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -1271,6 +1271,11 @@ static void v9fs_fix_path(V9fsPath *dst, V9fsPath *src, int len)
     dst->size++;
 }
 
+static inline bool is_ro_export(int export_flags)
+{
+    return export_flags & V9FS_RDONLY;
+}
+
 static void v9fs_version(void *opaque)
 {
     V9fsPDU *pdu = opaque;
@@ -1692,6 +1697,15 @@ static void v9fs_open(void *opaque)
         } else {
             flags = omode_to_uflags(mode);
         }
+        if (is_ro_export(s->ctx.export_flags)) {
+            if (mode & O_WRONLY || mode & O_RDWR ||
+                    mode & O_APPEND || mode & O_TRUNC) {
+                err = -EROFS;
+                goto out;
+            } else {
+                flags |= O_NOATIME;
+            }
+        }
         err = v9fs_co_open(pdu, fidp, flags);
         if (err < 0) {
             goto out;
@@ -3311,6 +3325,39 @@ static void v9fs_op_not_supp(void *opaque)
     complete_pdu(pdu->s, pdu, -EOPNOTSUPP);
 }
 
+static void v9fs_fs_ro(void *opaque)
+{
+    V9fsPDU *pdu = opaque;
+    complete_pdu(pdu->s, pdu, -EROFS);
+}
+
+static inline bool is_read_only_op(int id)
+{
+    switch (id) {
+    case P9_TREADDIR:
+    case P9_TSTATFS:
+    case P9_TGETATTR:
+    case P9_TXATTRWALK:
+    case P9_TLOCK:
+    case P9_TGETLOCK:
+    case P9_TREADLINK:
+    case P9_TVERSION:
+    case P9_TLOPEN:
+    case P9_TATTACH:
+    case P9_TSTAT:
+    case P9_TWALK:
+    case P9_TCLUNK:
+    case P9_TFSYNC:
+    case P9_TOPEN:
+    case P9_TREAD:
+    case P9_TAUTH:
+    case P9_TFLUSH:
+        return 1;
+    default:
+        return 0;
+    }
+}
+
 static void submit_pdu(V9fsState *s, V9fsPDU *pdu)
 {
     Coroutine *co;
@@ -3322,6 +3369,10 @@ static void submit_pdu(V9fsState *s, V9fsPDU *pdu)
     } else {
         handler = pdu_co_handlers[pdu->id];
     }
+
+    if (is_ro_export(s->ctx.export_flags) && !is_read_only_op(pdu->id)) {
+        handler = v9fs_fs_ro;
+    }
     co = qemu_coroutine_create(handler);
     qemu_coroutine_enter(co, pdu);
 }
diff --git a/qemu-config.c b/qemu-config.c
index 90b6b3e..597d7e1 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -180,7 +180,11 @@ QemuOptsList qemu_fsdev_opts = {
         }, {
             .name = "writeout",
             .type = QEMU_OPT_STRING,
+        }, {
+            .name = "readonly",
+            .type = QEMU_OPT_BOOL,
         },
+
         { /*End of list */ }
     },
 };
@@ -205,6 +209,9 @@ QemuOptsList qemu_virtfs_opts = {
         }, {
             .name = "writeout",
             .type = QEMU_OPT_STRING,
+        }, {
+            .name = "readonly",
+            .type = QEMU_OPT_BOOL,
         },
 
         { /*End of list */ }
diff --git a/vl.c b/vl.c
index c9de124..cf66ef9 100644
--- a/vl.c
+++ b/vl.c
@@ -2823,6 +2823,8 @@ int main(int argc, char **argv, char **envp)
                 qemu_opt_set(fsdev, "security_model",
                              qemu_opt_get(opts, "security_model"));
 
+                qemu_opt_set_bool(fsdev, "readonly",
+                                qemu_opt_get_bool(opts, "readonly", 0));
                 device = qemu_opts_create(qemu_find_opts("device"), NULL, 0);
                 qemu_opt_set(device, "driver", "virtio-9p-pci");
                 qemu_opt_set(device, "fsdev",
-- 
1.7.6