[Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache

[Qemu-devel] [PATCH 1/2] hw/9pfs: Add new virtfs option cache=writethrough to skip host page cache

[Aneesh Kumar K.V]

cache=writethrough implies the file are opened in the host with O_SYNC open flag

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 fsdev/file-op-9p.h         |    1 +
 fsdev/qemu-fsdev.c         |   10 ++++++++--
 fsdev/qemu-fsdev.h         |    2 ++
 hw/9pfs/virtio-9p-device.c |    6 ++++++
 hw/9pfs/virtio-9p.c        |   28 ++++++++++++++++++++--------
 qemu-config.c              |    6 ++++++
 qemu-options.hx            |   17 ++++++++++++-----
 vl.c                       |    6 ++++++
 8 files changed, 61 insertions(+), 15 deletions(-)

diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h
index 1eda342..fbf9afb 100644
--- a/fsdev/file-op-9p.h
+++ b/fsdev/file-op-9p.h
@@ -54,6 +54,7 @@ typedef struct FsContext
     char *fs_root;
     SecModel fs_sm;
     uid_t uid;
+    int open_flags;
     struct xattr_operations **xops;
 } FsContext;
 
diff --git a/fsdev/qemu-fsdev.c b/fsdev/qemu-fsdev.c
index 0b33290..fccf011 100644
--- a/fsdev/qemu-fsdev.c
+++ b/fsdev/qemu-fsdev.c
@@ -33,6 +33,8 @@ int qemu_fsdev_add(QemuOpts *opts)
     const char *fstype = qemu_opt_get(opts, "fstype");
     const char *path = qemu_opt_get(opts, "path");
     const char *sec_model = qemu_opt_get(opts, "security_model");
+    const char *cache = qemu_opt_get(opts, "cache");
+
 
     if (!fsdev_id) {
         fprintf(stderr, "fsdev: No id specified\n");
@@ -71,10 +73,14 @@ int qemu_fsdev_add(QemuOpts *opts)
     fsle->fse.path = qemu_strdup(path);
     fsle->fse.security_model = qemu_strdup(sec_model);
     fsle->fse.ops = FsTypes[i].ops;
-
+    fsle->fse.cache_model = 0;
+    if (cache) {
+        if (!strcmp(cache, "writethrough")) {
+            fsle->fse.cache_model = V9FS_WRITETHROUGH_CACHE;
+        }
+    }
     QTAILQ_INSERT_TAIL(&fstype_entries, fsle, next);
     return 0;
-
 }
 
 FsTypeEntry *get_fsdev_fsentry(char *id)
diff --git a/fsdev/qemu-fsdev.h b/fsdev/qemu-fsdev.h
index f9f08d3..8cc010b 100644
--- a/fsdev/qemu-fsdev.h
+++ b/fsdev/qemu-fsdev.h
@@ -34,6 +34,7 @@ typedef struct FsTypeTable {
     FileOperations *ops;
 } FsTypeTable;
 
+#define V9FS_WRITETHROUGH_CACHE 0x1
 /*
  * Structure to store the various fsdev's passed through command line.
  */
@@ -41,6 +42,7 @@ typedef struct FsTypeEntry {
     char *fsdev_id;
     char *path;
     char *security_model;
+    int cache_model;
     FileOperations *ops;
 } FsTypeEntry;
 
diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
index 4bec8bf..55edc45 100644
--- a/hw/9pfs/virtio-9p-device.c
+++ b/hw/9pfs/virtio-9p-device.c
@@ -114,6 +114,12 @@ VirtIODevice *virtio_9p_init(DeviceState *dev, V9fsConf *conf)
         exit(1);
     }
 
+    if (fse->cache_model & V9FS_WRITETHROUGH_CACHE) {
+        s->ctx.open_flags = O_SYNC;
+    } else {
+        s->ctx.open_flags = 0;
+    }
+
     s->ctx.fs_root = qemu_strdup(fse->path);
     len = strlen(conf->tag);
     if (len > MAX_TAG_LEN) {
diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index 55aca93..9d1813e 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -80,6 +80,22 @@ void cred_init(FsCred *credp)
     credp->fc_rdev = -1;
 }
 
+static int get_dotl_openflags(V9fsState *s, int oflags)
+{
+    int flags;
+    /*
+     * Filter the client open flags
+     */
+    flags = s->ctx.open_flags;
+    flags |= oflags;
+    flags &= ~(O_NOCTTY | O_ASYNC | O_CREAT);
+    /*
+     * Ignore direct disk access hint until the server supports it.
+     */
+    flags &= ~O_DIRECT;
+    return flags;
+}
+
 static void v9fs_string_init(V9fsString *str)
 {
     str->data = NULL;
@@ -1540,10 +1556,7 @@ static void v9fs_open(void *opaque)
         err = offset;
     } else {
         if (s->proto_version == V9FS_PROTO_2000L) {
-            flags = mode;
-            flags &= ~(O_NOCTTY | O_ASYNC | O_CREAT);
-            /* Ignore direct disk access hint until the server supports it. */
-            flags &= ~O_DIRECT;
+            flags = get_dotl_openflags(s, mode);
         } else {
             flags = omode_to_uflags(mode);
         }
@@ -1596,10 +1609,9 @@ static void v9fs_lcreate(void *opaque)
     }
     v9fs_string_sprintf(&fullname, "%s/%s", fidp->path.data, name.data);
 
-    /* Ignore direct disk access hint until the server supports it. */
-    flags &= ~O_DIRECT;
-
-    err = v9fs_co_open2(pdu->s, fidp, fullname.data, gid, flags, mode);
+    flags = get_dotl_openflags(pdu->s, flags);
+    err = v9fs_co_open2(pdu->s, fidp, fullname.data, gid,
+                        flags | O_CREAT, mode);
     if (err < 0) {
         goto out;
     }
diff --git a/qemu-config.c b/qemu-config.c
index 5d7ffa2..1125fb3 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -170,6 +170,9 @@ QemuOptsList qemu_fsdev_opts = {
         }, {
             .name = "security_model",
             .type = QEMU_OPT_STRING,
+        }, {
+            .name = "cache",
+            .type = QEMU_OPT_STRING,
         },
         { /*End of list */ }
     },
@@ -192,6 +195,9 @@ QemuOptsList qemu_virtfs_opts = {
         }, {
             .name = "security_model",
             .type = QEMU_OPT_STRING,
+        }, {
+            .name = "cache",
+            .type = QEMU_OPT_STRING,
         },
 
         { /*End of list */ }
diff --git a/qemu-options.hx b/qemu-options.hx
index 82e085a..4789fe4 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -486,7 +486,8 @@ ETEXI
 DEFHEADING(File system options:)
 
 DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
-    "-fsdev local,id=id,path=path,security_model=[mapped|passthrough|none]\n",
+    "-fsdev local,id=id,path=path,security_model=[mapped|passthrough|none]\n"
+    "       [,cache=writethrough]\n",
     QEMU_ARCH_ALL)
 
 STEXI
@@ -502,7 +503,7 @@ The specific Fstype will determine the applicable options.
 
 Options to each backend are described below.
 
-@item -fsdev local ,id=@var{id} ,path=@var{path} ,security_model=@var{security_model}
+@item -fsdev local ,id=@var{id} ,path=@var{path} ,security_model=@var{security_model}[,cache=@var{cache}]
 
 Create a file-system-"device" for local-filesystem.
 
@@ -513,13 +514,17 @@ Create a file-system-"device" for local-filesystem.
 @option{security_model} specifies the security model to be followed.
 @option{security_model} is required.
 
+@option{cache} specifies whether to skip the host page cache.
+@option{cache} is an optional argument.
+
 @end table
 ETEXI
 
 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",
+    "-virtfs local,path=path,mount_tag=tag,security_model=[mapped|passthrough|none]\n"
+    "        [,cache=writethrough]\n",
     QEMU_ARCH_ALL)
 
 STEXI
@@ -535,7 +540,7 @@ The specific Fstype will determine the applicable options.
 
 Options to each backend are described below.
 
-@item -virtfs local ,path=@var{path} ,mount_tag=@var{mount_tag} ,security_model=@var{security_model}
+@item -virtfs local ,path=@var{path} ,mount_tag=@var{mount_tag} ,security_model=@var{security_model}[,cache=@var{cache}]
 
 Create a Virtual file-system-pass through for local-filesystem.
 
@@ -546,10 +551,12 @@ Create a Virtual file-system-pass through for local-filesystem.
 @option{security_model} specifies the security model to be followed.
 @option{security_model} is required.
 
-
 @option{mount_tag} specifies the tag with which the exported file is mounted.
 @option{mount_tag} is required.
 
+@option{cache} specifies whether to skip the host page cache.
+@option{cache} is an optional argument.
+
 @end table
 ETEXI
 
diff --git a/vl.c b/vl.c
index b362871..396a8db 100644
--- a/vl.c
+++ b/vl.c
@@ -2541,6 +2541,7 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_virtfs: {
                 QemuOpts *fsdev;
                 QemuOpts *device;
+                const char *cache;
 
                 olist = qemu_find_opts("virtfs");
                 if (!olist) {
@@ -2570,6 +2571,11 @@ int main(int argc, char **argv, char **envp)
                             qemu_opt_get(opts, "mount_tag"));
                     exit(1);
                 }
+
+                cache = qemu_opt_get(opts, "cache");
+                if (cache) {
+                    qemu_opt_set(fsdev, "cache", cache);
+                }
                 qemu_opt_set(fsdev, "fstype", qemu_opt_get(opts, "fstype"));
                 qemu_opt_set(fsdev, "path", qemu_opt_get(opts, "path"));
                 qemu_opt_set(fsdev, "security_model",
-- 
1.7.4.1

[Qemu-devel] [PATCH 2/2] qemu-options.hx: Update virtfs command documentation

[Aneesh Kumar K.V]

Clarify the virtfs option better

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 qemu-options.hx |  116 ++++++++++++++++++++++++++++++++++---------------------
 1 files changed, 72 insertions(+), 44 deletions(-)

diff --git a/qemu-options.hx b/qemu-options.hx
index 4789fe4..c6fb12c 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -483,6 +483,8 @@ possible drivers and properties, use @code{-device ?} and
 @code{-device @var{driver},?}.
 ETEXI
 
+DEFHEADING()
+
 DEFHEADING(File system options:)
 
 DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
@@ -492,34 +494,54 @@ DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
 
 STEXI
 
-The general form of a File system device option is:
-@table @option
-
 @item -fsdev @var{fstype} ,id=@var{id} [,@var{options}]
 @findex -fsdev
-Fstype is one of:
-@option{local},
-The specific Fstype will determine the applicable options.
-
-Options to each backend are described below.
-
-@item -fsdev local ,id=@var{id} ,path=@var{path} ,security_model=@var{security_model}[,cache=@var{cache}]
-
-Create a file-system-"device" for local-filesystem.
 
-@option{local} is only available on Linux.
-
-@option{path} specifies the path to be exported. @option{path} is required.
+Define a new file system device. Valid options are
+@table @option
+@item local
+This option create a file-system-"device" for local-filesystem.
+Currently only local file system device is supported.
+@item id=@var{id}
+Identifier for this device
+@item path=@var{path}
+This option define the export path for the file system device.
+Files below this path will be available for 9p client on the
+guest.
+@item security_model=@var{security_model}
+This option define the security model to be used when exporting
+the files. The supported security models are passthrough, mapped
+and none. In passthrough security model, file are stored using
+the same credentials as they are created on the guest. This require
+qemu to run as root. In the mapped security model, some of the
+file attributes like uid, gid, mode bits and link target are
+stored as file attributes. Directories exported by this security
+model cannot interact with other unix tools. "none" security model
+is same as passthrough expect they won't report failures if
+the sever fails to set file attributes like ownership.
+@item cache=@var{cache}
+This is an optional argument. The support value is writethrough
+This means thatthe 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.
 
-@option{security_model} specifies the security model to be followed.
-@option{security_model} is required.
+@end table
 
-@option{cache} specifies whether to skip the host page cache.
-@option{cache} is an optional argument.
+-fsdev option is used along with -device driver "virtio-9p-pci"
+Option for virtio-9p-pci driver are
 
+@table @option
+@item fsdev=@var{id}
+This option specify the @var{id} value specified along with -fsdev option
+@item mount_tag=@var{mount_tag}
+This option specifies the tag name to be used by the guest
+to mount this export point
 @end table
+
 ETEXI
 
+DEFHEADING()
+
 DEFHEADING(Virtual File system pass-through options:)
 
 DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
@@ -529,33 +551,39 @@ DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
 
 STEXI
 
-The general form of a Virtual File system pass-through option is:
-@table @option
-
-@item -virtfs @var{fstype} [,@var{options}]
-@findex -virtfs
-Fstype is one of:
-@option{local},
-The specific Fstype will determine the applicable options.
-
-Options to each backend are described below.
-
 @item -virtfs local ,path=@var{path} ,mount_tag=@var{mount_tag} ,security_model=@var{security_model}[,cache=@var{cache}]
+@findex -virtfs
 
-Create a Virtual file-system-pass through for local-filesystem.
-
-@option{local} is only available on Linux.
-
-@option{path} specifies the path to be exported. @option{path} is required.
-
-@option{security_model} specifies the security model to be followed.
-@option{security_model} is required.
-
-@option{mount_tag} specifies the tag with which the exported file is mounted.
-@option{mount_tag} is required.
-
-@option{cache} specifies whether to skip the host page cache.
-@option{cache} is an optional argument.
+The general form of a Virtual File system pass-through option is:
+@table @option
+@item local
+This option create a file-system-"device" for local-filesystem.
+Currently only local file system device is supported.
+@item id=@var{id}
+Identifier for this device
+@item path=@var{path}
+This option define the export path for the file system device.
+Files below this path will be available for 9p client on the
+guest.
+@item mount_tag=@var{mount_tag}
+This option specifies the tag name to be used by the guest
+to mount this export point
+@item security_model=@var{security_model}
+This option define the security model to be used when exporting
+the files. The supported security models are passthrough, mapped
+and none. In passthrough security model, file are stored using
+the same credentials as they are created on the guest. This require
+qemu to run as root. In the mapped security model, some of the
+file attributes like uid, gid, mode bits and link target are
+stored as file attributes. Directories exported by this security
+model cannot interact with other unix tools. "none" security model
+is same as passthrough expect they won't report failures if
+the sever fails to set file attributes like ownership.
+@item cache=@var{cache}
+This is an optional argument. The support value is writethrough
+This means thatthe 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.
 
 @end table
 ETEXI
-- 
1.7.4.1

Re: [Qemu-devel] [PATCH 2/2] qemu-options.hx: Update virtfs command documentation

[Markus Armbruster]

"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> writes:

> Clarify the virtfs option better
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  qemu-options.hx |  116 ++++++++++++++++++++++++++++++++++---------------------
>  1 files changed, 72 insertions(+), 44 deletions(-)
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 4789fe4..c6fb12c 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -483,6 +483,8 @@ possible drivers and properties, use @code{-device ?} and
>  @code{-device @var{driver},?}.
>  ETEXI
>  
> +DEFHEADING()
> +
>  DEFHEADING(File system options:)
>  
>  DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
> @@ -492,34 +494,54 @@ DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
>  
>  STEXI
>  
> -The general form of a File system device option is:
> -@table @option
> -
>  @item -fsdev @var{fstype} ,id=@var{id} [,@var{options}]
>  @findex -fsdev
> -Fstype is one of:
> -@option{local},
> -The specific Fstype will determine the applicable options.
> -
> -Options to each backend are described below.
> -
> -@item -fsdev local ,id=@var{id} ,path=@var{path} ,security_model=@var{security_model}[,cache=@var{cache}]
> -
> -Create a file-system-"device" for local-filesystem.
>  
> -@option{local} is only available on Linux.
> -
> -@option{path} specifies the path to be exported. @option{path} is required.
> +Define a new file system device. Valid options are
> +@table @option
> +@item local
> +This option create a file-system-"device" for local-filesystem.
> +Currently only local file system device is supported.
> +@item id=@var{id}
> +Identifier for this device
> +@item path=@var{path}
> +This option define the export path for the file system device.
> +Files below this path will be available for 9p client on the
> +guest.
> +@item security_model=@var{security_model}
> +This option define the security model to be used when exporting
> +the files. The supported security models are passthrough, mapped
> +and none. In passthrough security model, file are stored using
> +the same credentials as they are created on the guest. This require
> +qemu to run as root. In the mapped security model, some of the
> +file attributes like uid, gid, mode bits and link target are
> +stored as file attributes. Directories exported by this security
> +model cannot interact with other unix tools. "none" security model
> +is same as passthrough expect they won't report failures if

"expect"?  "except"?

> +the sever fails to set file attributes like ownership.
> +@item cache=@var{cache}
> +This is an optional argument. The support value is writethrough

"The support value"?  "The only supported value"?

> +This means thatthe host page cache will be used to read and write

"thatthe"  Use a spell-checker, please.

> +data but write notification will be sent to the guest only when
> +the data has been reported as written by the storage subsystem.
>  
> -@option{security_model} specifies the security model to be followed.
> -@option{security_model} is required.
> +@end table
>  
> -@option{cache} specifies whether to skip the host page cache.
> -@option{cache} is an optional argument.
> +-fsdev option is used along with -device driver "virtio-9p-pci"
> +Option for virtio-9p-pci driver are

Options (plural).

>  
> +@table @option
> +@item fsdev=@var{id}
> +This option specify the @var{id} value specified along with -fsdev option
> +@item mount_tag=@var{mount_tag}
> +This option specifies the tag name to be used by the guest
> +to mount this export point
>  @end table
> +
>  ETEXI
>  
> +DEFHEADING()
> +
>  DEFHEADING(Virtual File system pass-through options:)
>  
>  DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
> @@ -529,33 +551,39 @@ DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
>  
>  STEXI
>  
> -The general form of a Virtual File system pass-through option is:
> -@table @option
> -
> -@item -virtfs @var{fstype} [,@var{options}]
> -@findex -virtfs
> -Fstype is one of:
> -@option{local},
> -The specific Fstype will determine the applicable options.
> -
> -Options to each backend are described below.
> -
>  @item -virtfs local ,path=@var{path} ,mount_tag=@var{mount_tag} ,security_model=@var{security_model}[,cache=@var{cache}]
> +@findex -virtfs
>  
> -Create a Virtual file-system-pass through for local-filesystem.
> -
> -@option{local} is only available on Linux.
> -
> -@option{path} specifies the path to be exported. @option{path} is required.
> -
> -@option{security_model} specifies the security model to be followed.
> -@option{security_model} is required.
> -
> -@option{mount_tag} specifies the tag with which the exported file is mounted.
> -@option{mount_tag} is required.
> -
> -@option{cache} specifies whether to skip the host page cache.
> -@option{cache} is an optional argument.
> +The general form of a Virtual File system pass-through option is:
> +@table @option
> +@item local
> +This option create a file-system-"device" for local-filesystem.
> +Currently only local file system device is supported.
> +@item id=@var{id}
> +Identifier for this device
> +@item path=@var{path}
> +This option define the export path for the file system device.
> +Files below this path will be available for 9p client on the
> +guest.
> +@item mount_tag=@var{mount_tag}
> +This option specifies the tag name to be used by the guest
> +to mount this export point
> +@item security_model=@var{security_model}
> +This option define the security model to be used when exporting
> +the files. The supported security models are passthrough, mapped
> +and none. In passthrough security model, file are stored using
> +the same credentials as they are created on the guest. This require
> +qemu to run as root. In the mapped security model, some of the
> +file attributes like uid, gid, mode bits and link target are
> +stored as file attributes. Directories exported by this security
> +model cannot interact with other unix tools. "none" security model
> +is same as passthrough expect they won't report failures if
> +the sever fails to set file attributes like ownership.
> +@item cache=@var{cache}
> +This is an optional argument. The support value is writethrough
> +This means thatthe 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.

Same typos as above.

>  
>  @end table
>  ETEXI

[Qemu-devel] [PATCH 2/2] qemu-options.hx: Update virtfs command documentation

[Aneesh Kumar K.V]

Clarify the virtfs option better
Updates from:Sripathi Kodi <sripathik@in.ibm.com>

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 qemu-options.hx |  119 ++++++++++++++++++++++++++++++++-----------------------
 1 files changed, 69 insertions(+), 50 deletions(-)

diff --git a/qemu-options.hx b/qemu-options.hx
index 38f0aef..6c744e0 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -522,43 +522,61 @@ possible drivers and properties, use @code{-device ?} and
 @code{-device @var{driver},?}.
 ETEXI
 
+DEFHEADING()
+
 DEFHEADING(File system options:)
 
 DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
-    "-fsdev local,id=id,path=path,security_model=[mapped|passthrough|none]\n"
+    "-fsdev fsdriver,id=id,path=path,security_model=[mapped|passthrough|none]\n"
     "       [,cache=writethrough]\n",
     QEMU_ARCH_ALL)
 
 STEXI
 
-The general form of a File system device option is:
-@table @option
-
-@item -fsdev @var{fstype} ,id=@var{id} [,@var{options}]
+@item -fsdev @var{fsdriver},id=@var{id},path=@var{path},security_model=@var{security_model}[,cache=@var{cache}]
 @findex -fsdev
-Fstype is one of:
-@option{local},
-The specific Fstype will determine the applicable options.
-
-Options to each backend are described below.
-
-@item -fsdev local ,id=@var{id} ,path=@var{path} ,security_model=@var{security_model}[,cache=@var{cache}]
-
-Create a file-system-"device" for local-filesystem.
-
-@option{local} is only available on Linux.
-
-@option{path} specifies the path to be exported. @option{path} is required.
-
-@option{security_model} specifies the security model to be followed.
-@option{security_model} is required.
-
-@option{cache} specifies whether to skip the host page cache.
-@option{cache} is an optional argument.
+Define a new file system device. Valid options are:
+@table @option
+@item @var{fsdriver}
+This option specifies the fs driver backend to use.
+Currently "local" and "handle" file system drivers are supported.
+@item id=@var{id}
+Specifies identifier for this device
+@item path=@var{path}
+Specifies the export path for the file system device. Files under
+this path will be available to the 9p client on the guest.
+@item security_model=@var{security_model}
+Specifies the security model to be used for this export path.
+Supported security models are "passthrough", "mapped" and "none".
+In "passthrough" security model, files are stored using the same
+credentials as they are created on the guest. This requires qemu
+to run as root. In "mapped" security model, some of the file
+attributes like uid, gid, mode bits and link target are stored as
+file attributes. Directories exported by this security model cannot
+interact with other unix tools. "none" security model is same as
+passthrough except the sever won't report failures if it fails to
+set file attributes like ownership.
+@item cache=@var{cache}
+This is an optional argument. The only supported value is "writethrough".
+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.
+@end table
 
+-fsdev option is used along with -device driver "virtio-9p-pci".
+@item -device virtio-9p-pci,fsdev=@var{id},mount_tag=@var{mount_tag}
+Options for virtio-9p-pci driver are:
+@table @option
+@item fsdev=@var{id}
+Specifies the id value specified along with -fsdev option
+@item mount_tag=@var{mount_tag}
+Specifies the tag name to be used by the guest to mount this export point
 @end table
+
 ETEXI
 
+DEFHEADING()
+
 DEFHEADING(Virtual File system pass-through options:)
 
 DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
@@ -568,34 +586,35 @@ DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
 
 STEXI
 
-The general form of a Virtual File system pass-through option is:
-@table @option
-
-@item -virtfs @var{fstype} [,@var{options}]
+@item -virtfs @var{fsdriver},path=@var{path},mount_tag=@var{mount_tag},security_model=@var{security_model}[,cache=@var{cache}]
 @findex -virtfs
-Fstype is one of:
-@option{local},
-The specific Fstype will determine the applicable options.
-
-Options to each backend are described below.
-
-@item -virtfs local ,path=@var{path} ,mount_tag=@var{mount_tag} ,security_model=@var{security_model}[,cache=@var{cache}]
-
-Create a Virtual file-system-pass through for local-filesystem.
-
-@option{local} is only available on Linux.
-
-@option{path} specifies the path to be exported. @option{path} is required.
-
-@option{security_model} specifies the security model to be followed.
-@option{security_model} is required.
-
-@option{mount_tag} specifies the tag with which the exported file is mounted.
-@option{mount_tag} is required.
-
-@option{cache} specifies whether to skip the host page cache.
-@option{cache} is an optional argument.
 
+The general form of a Virtual File system pass-through options are:
+@table @option
+@item @var{fsdriver}
+This option specifies the fs driver backend to use.
+Currently "local" and "handle" file system drivers are supported.
+@item id=@var{id}
+Specifies identifier for this device
+@item path=@var{path}
+Specifies the export path for the file system device. Files under
+this path will be available to the 9p client on the guest.
+@item security_model=@var{security_model}
+Specifies the security model to be used for this export path.
+Supported security models are "passthrough", "mapped" and "none".
+In "passthrough" security model, files are stored using the same
+credentials as they are created on the guest. This requires qemu
+to run as root. In "mapped" security model, some of the file
+attributes like uid, gid, mode bits and link target are stored as
+file attributes. Directories exported by this security model cannot
+interact with other unix tools. "none" security model is same as
+passthrough except the sever won't report failures if it fails to
+set file attributes like ownership.
+@item cache=@var{cache}
+This is an optional argument. The only supported value is "writethrough".
+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.
 @end table
 ETEXI
 
-- 
1.7.4.1