[Qemu-devel] [PATCH] hw/9pfs: Use little-endian format for xattr values

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

With security_model=mapped-xattr, we encode the uid,gid and other file
attributes as extended attributes of the file. We save them under
user.virtfs.* namespace.

Use little-endian encoding for on-disk values. This enables us to export
the same directory from both little-endian and big-endian hosts.

NOTE: This will break big-endian host that have virtFS exports
using security model mapped-xattr. They will have to use external tools
to convert the xattr to little-endian format.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 hw/9pfs/virtio-9p-local.c | 44 ++++++++++++++++++++------------------------
 1 file changed, 20 insertions(+), 24 deletions(-)

diff --git a/hw/9pfs/virtio-9p-local.c b/hw/9pfs/virtio-9p-local.c
index 3b0b6a9b1d7d..2787ddbe1f5e 100644
--- a/hw/9pfs/virtio-9p-local.c
+++ b/hw/9pfs/virtio-9p-local.c
@@ -135,17 +135,17 @@ static int local_lstat(FsContext *fs_ctx, V9fsPath *fs_path, struct stat *stbuf)
         mode_t tmp_mode;
         dev_t tmp_dev;
         if (getxattr(buffer, "user.virtfs.uid", &tmp_uid, sizeof(uid_t)) > 0) {
-            stbuf->st_uid = tmp_uid;
+            stbuf->st_uid = le32_to_cpu(tmp_uid);
         }
         if (getxattr(buffer, "user.virtfs.gid", &tmp_gid, sizeof(gid_t)) > 0) {
-            stbuf->st_gid = tmp_gid;
+            stbuf->st_gid = le32_to_cpu(tmp_gid);
         }
         if (getxattr(buffer, "user.virtfs.mode",
                     &tmp_mode, sizeof(mode_t)) > 0) {
-            stbuf->st_mode = tmp_mode;
+            stbuf->st_mode = le32_to_cpu(tmp_mode);
         }
         if (getxattr(buffer, "user.virtfs.rdev", &tmp_dev, sizeof(dev_t)) > 0) {
-                stbuf->st_rdev = tmp_dev;
+            stbuf->st_rdev = le64_to_cpu(tmp_dev);
         }
     } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
         local_mapped_file_attr(fs_ctx, path, stbuf);
@@ -255,29 +255,29 @@ static int local_set_xattr(const char *path, FsCred *credp)
     int err;
 
     if (credp->fc_uid != -1) {
-        err = setxattr(path, "user.virtfs.uid", &credp->fc_uid, sizeof(uid_t),
-                0);
+        uint32_t tmp_uid = cpu_to_le32(credp->fc_uid);
+        err = setxattr(path, "user.virtfs.uid", &tmp_uid, sizeof(uid_t), 0);
         if (err) {
             return err;
         }
     }
     if (credp->fc_gid != -1) {
-        err = setxattr(path, "user.virtfs.gid", &credp->fc_gid, sizeof(gid_t),
-                0);
+        uint32_t tmp_gid = cpu_to_le32(credp->fc_gid);
+        err = setxattr(path, "user.virtfs.gid", &tmp_gid, sizeof(gid_t), 0);
         if (err) {
             return err;
         }
     }
     if (credp->fc_mode != -1) {
-        err = setxattr(path, "user.virtfs.mode", &credp->fc_mode,
-                sizeof(mode_t), 0);
+        uint32_t tmp_mode = cpu_to_le32(credp->fc_mode);
+        err = setxattr(path, "user.virtfs.mode", &tmp_mode, sizeof(mode_t), 0);
         if (err) {
             return err;
         }
     }
     if (credp->fc_rdev != -1) {
-        err = setxattr(path, "user.virtfs.rdev", &credp->fc_rdev,
-                sizeof(dev_t), 0);
+        uint64_t tmp_rdev = cpu_to_le64(credp->fc_rdev);
+        err = setxattr(path, "user.virtfs.rdev", &tmp_rdev, sizeof(dev_t), 0);
         if (err) {
             return err;
         }
@@ -630,21 +630,17 @@ static int local_fstat(FsContext *fs_ctx, int fid_type,
         mode_t tmp_mode;
         dev_t tmp_dev;
 
-        if (fgetxattr(fd, "user.virtfs.uid",
-                      &tmp_uid, sizeof(uid_t)) > 0) {
-            stbuf->st_uid = tmp_uid;
+        if (fgetxattr(fd, "user.virtfs.uid", &tmp_uid, sizeof(uid_t)) > 0) {
+            stbuf->st_uid = le32_to_cpu(tmp_uid);
         }
-        if (fgetxattr(fd, "user.virtfs.gid",
-                      &tmp_gid, sizeof(gid_t)) > 0) {
-            stbuf->st_gid = tmp_gid;
+        if (fgetxattr(fd, "user.virtfs.gid", &tmp_gid, sizeof(gid_t)) > 0) {
+            stbuf->st_gid = le32_to_cpu(tmp_gid);
         }
-        if (fgetxattr(fd, "user.virtfs.mode",
-                      &tmp_mode, sizeof(mode_t)) > 0) {
-            stbuf->st_mode = tmp_mode;
+        if (fgetxattr(fd, "user.virtfs.mode", &tmp_mode, sizeof(mode_t)) > 0) {
+            stbuf->st_mode = le32_to_cpu(tmp_mode);
         }
-        if (fgetxattr(fd, "user.virtfs.rdev",
-                      &tmp_dev, sizeof(dev_t)) > 0) {
-                stbuf->st_rdev = tmp_dev;
+        if (fgetxattr(fd, "user.virtfs.rdev", &tmp_dev, sizeof(dev_t)) > 0) {
+            stbuf->st_rdev = le64_to_cpu(tmp_dev);
         }
     } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
         errno = EOPNOTSUPP;
-- 
1.9.1