path: root/fs/fs_context.c
diff options
authorDavid Howells <>2018-11-01 23:33:31 +0000
committerAl Viro <>2019-03-20 18:49:06 -0400
commit24dcb3d90a1f67fe08c68a004af37df059d74005 (patch)
tree14f5bfaf1a0d7dcb56a1d2217d4ce13d1e447dea /fs/fs_context.c
parentdadd2299ab61fc2b55b95b7b3a8f674cdd3b69c9 (diff)
vfs: syscall: Add fsopen() to prepare for superblock creation
Provide an fsopen() system call that starts the process of preparing to create a superblock that will then be mountable, using an fd as a context handle. fsopen() is given the name of the filesystem that will be used: int mfd = fsopen(const char *fsname, unsigned int flags); where flags can be 0 or FSOPEN_CLOEXEC. For example: sfd = fsopen("ext4", FSOPEN_CLOEXEC); fsconfig(sfd, FSCONFIG_SET_PATH, "source", "/dev/sda1", AT_FDCWD); fsconfig(sfd, FSCONFIG_SET_FLAG, "noatime", NULL, 0); fsconfig(sfd, FSCONFIG_SET_FLAG, "acl", NULL, 0); fsconfig(sfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0); fsconfig(sfd, FSCONFIG_SET_STRING, "sb", "1", 0); fsconfig(sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0); fsinfo(sfd, NULL, ...); // query new superblock attributes mfd = fsmount(sfd, FSMOUNT_CLOEXEC, MS_RELATIME); move_mount(mfd, "", sfd, AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH); sfd = fsopen("afs", -1); fsconfig(fd, FSCONFIG_SET_STRING, "source", "", 0); fsconfig(fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0); mfd = fsmount(sfd, 0, MS_NODEV); move_mount(mfd, "", sfd, AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH); If an error is reported at any step, an error message may be available to be read() back (ENODATA will be reported if there isn't an error available) in the form: "e <subsys>:<problem>" "e SELinux:Mount on mountpoint not permitted" Once fsmount() has been called, further fsconfig() calls will incur EBUSY, even if the fsmount() fails. read() is still possible to retrieve error information. The fsopen() syscall creates a mount context and hangs it of the fd that it returns. Netlink is not used because it is optional and would make the core VFS dependent on the networking layer and also potentially add network namespace issues. Note that, for the moment, the caller must have SYS_CAP_ADMIN to use fsopen(). Signed-off-by: David Howells <> cc: Signed-off-by: Al Viro <>
Diffstat (limited to 'fs/fs_context.c')
1 files changed, 4 insertions, 0 deletions
diff --git a/fs/fs_context.c b/fs/fs_context.c
index 87e3546b9a52..eb806fae3117 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -271,6 +271,8 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
fc->cred = get_current_cred();
fc->net_ns = get_net(current->nsproxy->net_ns);
+ mutex_init(&fc->uapi_mutex);
switch (purpose) {
fc->user_ns = get_user_ns(fc->cred->user_ns);
@@ -353,6 +355,8 @@ struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
if (!fc)
return ERR_PTR(-ENOMEM);
+ mutex_init(&fc->uapi_mutex);
fc->fs_private = NULL;
fc->s_fs_info = NULL;
fc->source = NULL;