hw/9pfs: Read-only support for 9p export

A new fsdev parameter "readonly" is introduced to control accessing 9p export.
"readonly" 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>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

6 files changed, 78 insertions, 6 deletions

diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h
index 908e2a5edc..5788ff911c 100644
--- a/fsdev/file-op-9p.h
+++ b/fsdev/file-op-9p.h
@@ -56,10 +56,12 @@ typedef struct extended_ops {
  * On failure ignore the error.
  */
 #define V9FS_SM_NONE                0x00000010
-
+#define V9FS_RDONLY                 0x00000020
 
 #define V9FS_SEC_MASK               0x0000001C
 
+
+
 typedef struct FsContext
 {
     uid_t uid;
diff --git a/fsdev/qemu-fsdev.c b/fsdev/qemu-fsdev.c
index 5977bcca4c..27d10cb3b3 100644
--- a/fsdev/qemu-fsdev.c
+++ b/fsdev/qemu-fsdev.c
@@ -35,7 +35,7 @@ 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");
@@ -86,6 +86,11 @@ 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 8b6813f8de..e7618d72ba 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(FsContext *ctx)
+{
+    return ctx->export_flags & V9FS_RDONLY;
+}
+
 static void v9fs_version(void *opaque)
 {
     V9fsPDU *pdu = opaque;
@@ -1690,6 +1695,14 @@ static void v9fs_open(void *opaque)
         } else {
             flags = omode_to_uflags(mode);
         }
+        if (is_ro_export(&s->ctx)) {
+            if (mode & O_WRONLY || mode & O_RDWR ||
+                mode & O_APPEND || mode & O_TRUNC) {
+                err = -EROFS;
+                goto out;
+            }
+            flags |= O_NOATIME;
+        }
         err = v9fs_co_open(pdu, fidp, flags);
         if (err < 0) {
             goto out;
@@ -3309,6 +3322,39 @@ 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(V9fsPDU *pdu)
+{
+    switch (pdu->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;
@@ -3320,6 +3366,10 @@ static void submit_pdu(V9fsState *s, V9fsPDU *pdu)
     } else {
         handler = pdu_co_handlers[pdu->id];
     }
+
+    if (is_ro_export(&s->ctx) && !is_read_only_op(pdu)) {
+        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 90b6b3e85b..597d7e10b1 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/qemu-options.hx b/qemu-options.hx
index 5d2a7765e8..1baa381ab9 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -528,12 +528,12 @@ DEFHEADING(File system options:)
 
 DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
     "-fsdev fsdriver,id=id,path=path,[security_model={mapped|passthrough|none}]\n"
-    "       [,writeout=immediate]\n",
+    "       [,writeout=immediate][,readonly]\n",
     QEMU_ARCH_ALL)
 
 STEXI
 
-@item -fsdev @var{fsdriver},id=@var{id},path=@var{path},[security_model=@var{security_model}][,writeout=@var{writeout}]
+@item -fsdev @var{fsdriver},id=@var{id},path=@var{path},[security_model=@var{security_model}][,writeout=@var{writeout}][,readonly]
 @findex -fsdev
 Define a new file system device. Valid options are:
 @table @option
@@ -563,6 +563,9 @@ This is an optional argument. The only supported value is "immediate".
 This means that host page cache will be used to read and write data but
 write notification will be sent to the guest only when the data has been
 reported as written by the storage subsystem.
+@item readonly
+Enables exporting 9p share as a readonly mount for guests. By default
+read-write access is given.
 @end table
 
 -fsdev option is used along with -device driver "virtio-9p-pci".
@@ -583,12 +586,12 @@ DEFHEADING(Virtual File system pass-through options:)
 
 DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
     "-virtfs local,path=path,mount_tag=tag,security_model=[mapped|passthrough|none]\n"
-    "        [,writeout=immediate]\n",
+    "        [,writeout=immediate][,readonly]\n",
     QEMU_ARCH_ALL)
 
 STEXI
 
-@item -virtfs @var{fsdriver},path=@var{path},mount_tag=@var{mount_tag},security_model=@var{security_model}[,writeout=@var{writeout}]
+@item -virtfs @var{fsdriver},path=@var{path},mount_tag=@var{mount_tag},security_model=@var{security_model}[,writeout=@var{writeout}][,readonly]
 @findex -virtfs
 
 The general form of a Virtual File system pass-through options are:
@@ -619,6 +622,9 @@ This is an optional argument. The only supported value is "immediate".
 This means that host page cache will be used to read and write data but
 write notification will be sent to the guest only when the data has been
 reported as written by the storage subsystem.
+@item readonly
+Enables exporting 9p share as a readonly mount for guests. By default
+read-write access is given.
 @end table
 ETEXI
 
diff --git a/vl.c b/vl.c
index 1ddb17bfd9..c51a7403cb 100644
--- a/vl.c
+++ b/vl.c
@@ -2707,6 +2707,8 @@ 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",