[RFC PATCH v4 20/36] fuse-bpf: Add symlink/link support

Daniel Rosenberg
2024-03-29T01:54:44Z

This adds backing support for FUSE_LINK, FUSE_READLINK, and FUSE_SYMLINK

Signed-off-by: Daniel Rosenberg <drosen@google.com
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
fs/fuse/backing.c | 327 ++++++++++++++++++++++++++++++++++++++++++++++
fs/fuse/dir.c | 11 ++
fs/fuse/fuse_i.h | 20 +++
3 files changed, 358 insertions(+)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index 3390ce66e393..f18aee297335 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -2490,6 +2490,125 @@ int fuse_bpf_unlink(int *out, struct inode *dir, struct dentry *entry)
dir, entry);
}

+struct fuse_link_args {
+ struct fuse_link_in in;
+ struct fuse_buffer name;
+};
+
+static int fuse_link_initialize_in(struct bpf_fuse_args *fa, struct fuse_link_args *args,
+ struct dentry *entry, struct inode *dir,
+ struct dentry *newent)
+{
+ struct inode *src_inode = entry->d_inode;
+
+ *args = (struct fuse_link_args) {
+ .in = (struct fuse_link_in) {
+ .oldnodeid = get_node_id(src_inode),
+ },
+ .name = (struct fuse_buffer) {
+ .data = (void *) newent->d_name.name,
+ .size = newent->d_name.len + 1,
+ .max_size = NAME_MAX + 1,
+ .flags = BPF_FUSE_VARIABLE_SIZE | BPF_FUSE_MUST_ALLOCATE,
+ },
+ };
+
+ *fa = (struct bpf_fuse_args) {
+ .info = (struct bpf_fuse_meta_info) {
+ .opcode = FUSE_LINK,
+ },
+ .in_numargs = 2,
+ .in_args[0] = (struct bpf_fuse_arg) {
+ .size = sizeof(args->in),
+ .value = &args->in,
+ },
+ .in_args[1] = (struct bpf_fuse_arg) {
+ .is_buffer = true,
+ .buffer = &args->name,
+ },
+ };
+
+ return 0;
+}
+
+static int fuse_link_initialize_out(struct bpf_fuse_args *fa, struct fuse_link_args *args,
+ struct dentry *entry, struct inode *dir,
+ struct dentry *newent)
+{
+ return 0;
+}
+
+static int fuse_link_backing(struct bpf_fuse_args *fa, int *out, struct dentry *entry,
+ struct inode *dir, struct dentry *newent)
+{
+ struct path backing_old_path;
+ struct path backing_new_path;
+ struct dentry *backing_dir_dentry;
+ struct inode *fuse_new_inode = NULL;
+ struct fuse_inode *fuse_dir_inode = get_fuse_inode(dir);
+ struct inode *backing_dir_inode = fuse_dir_inode->backing_inode;
+
+ *out = 0;
+ get_fuse_backing_path(entry, &backing_old_path);
+ if (!backing_old_path.dentry)
+ return -EBADF;
+
+ get_fuse_backing_path(newent, &backing_new_path);
+ if (!backing_new_path.dentry) {
+ *out = -EBADF;
+ goto err_dst_path;
+ }
+
+ backing_dir_dentry = dget_parent(backing_new_path.dentry);
+ backing_dir_inode = d_inode(backing_dir_dentry);
+
+ inode_lock_nested(backing_dir_inode, I_MUTEX_PARENT);
+ *out = vfs_link(backing_old_path.dentry, &nop_mnt_idmap,
+ backing_dir_inode, backing_new_path.dentry, NULL);
+ inode_unlock(backing_dir_inode);
+ if (*out)
+ goto out;
+
+ if (d_really_is_negative(backing_new_path.dentry) ||
+ unlikely(d_unhashed(backing_new_path.dentry))) {
+ *out = -EINVAL;
+ /**
+ * TODO: overlayfs responds to this situation with a
+ * lookupOneLen. Should we do that too?
+ */
+ goto out;
+ }
+
+ fuse_new_inode = fuse_iget_backing(dir->i_sb, fuse_dir_inode->nodeid, backing_dir_inode);
+ if (IS_ERR(fuse_new_inode)) {
+ *out = PTR_ERR(fuse_new_inode);
+ goto out;
+ }
+ d_instantiate(newent, fuse_new_inode);
+
+out:
+ dput(backing_dir_dentry);
+ path_put(&backing_new_path);
+err_dst_path:
+ path_put(&backing_old_path);
+ return *out;
+}
+
+static int fuse_link_finalize(struct bpf_fuse_args *fa, int *out, struct dentry *entry,
+ struct inode *dir, struct dentry *newent)
+{
+ return 0;
+}
+
+int fuse_bpf_link(int *out, struct inode *inode, struct dentry *entry,
+ struct inode *newdir, struct dentry *newent)
+{
+ return bpf_fuse_backing(inode, struct fuse_link_args, out,
+ fuse_link_initialize_in, fuse_link_initialize_out,
+ fuse_link_backing, fuse_link_finalize,
+ entry, newdir, newent);
+}
+
struct fuse_getattr_args {
struct fuse_getattr_in in;
struct fuse_attr_out out;
@@ -2786,6 +2905,214 @@ int fuse_bpf_statfs(int *out, struct inode *inode, struct dentry *dentry, struct
dentry, buf);
}

+struct fuse_get_link_args {
+ struct fuse_buffer name;
+ struct fuse_buffer path;
+};
+
+static int fuse_get_link_initialize_in(struct bpf_fuse_args *fa, struct fuse_get_link_args *args,
+ struct inode *inode, struct dentry *dentry,
+ struct delayed_call *callback)
+{
+ /*
+ * TODO
+ * If we want to handle changing these things, we'll need to copy
+ * the lower fs's data into our own buffer, and provide our own callback
+ * to free that buffer.
+ *
+ * Pre could change the name we're looking at
+ * postfilter can change the name we return
+ *
+ * We ought to only make that buffer if it's been requested, so leaving
+ * this unimplemented for the moment
+ */
+ *args = (struct fuse_get_link_args) {
+ .name = (struct fuse_buffer) {
+ .data = (void *) dentry->d_name.name,
+ .size = dentry->d_name.len + 1,
+ .max_size = NAME_MAX + 1,
+ .flags = BPF_FUSE_VARIABLE_SIZE | BPF_FUSE_MUST_ALLOCATE,
+ },
+ };
+
+ *fa = (struct bpf_fuse_args) {
+ .info = (struct bpf_fuse_meta_info) {
+ .opcode = FUSE_READLINK,
+ .nodeid = get_node_id(inode),
+ },
+ .in_numargs = 1,
+ .in_args[0] = (struct bpf_fuse_arg) {
+ .is_buffer = true,
+ .buffer = &args->name,
+ },
+ };
+
+ return 0;
+}
+
+static int fuse_get_link_initialize_out(struct bpf_fuse_args *fa, struct fuse_get_link_args *args,
+ struct inode *inode, struct dentry *dentry,
+ struct delayed_call *callback)
+{
+ // TODO
+#if 0
+ args->path = (struct fuse_buffer) {
+ .data = NULL,
+ .size = 0,
+ .max_size = PATH_MAX,
+ .flags = BPF_FUSE_VARIABLE_SIZE | BPF_FUSE_MUST_ALLOCATE,
+ };
+ fa->out_numargs = 1;
+ fa->out_args[0].is_buffer = true;
+ fa->out_args[0].buffer = &args->path;
+#endif
+
+ return 0;
+}
+
+static int fuse_get_link_backing(struct bpf_fuse_args *fa, const char **out,
+ struct inode *inode, struct dentry *dentry,
+ struct delayed_call *callback)
+{
+ struct path backing_path;
+
+ if (!dentry) {
+ *out = ERR_PTR(-ECHILD);
+ return PTR_ERR(*out);
+ }
+
+ get_fuse_backing_path(dentry, &backing_path);
+ if (!backing_path.dentry) {
+ *out = ERR_PTR(-ECHILD);
+ return PTR_ERR(*out);
+ }
+
+ /*
+ * TODO: If we want to do our own thing, copy the data and then call the
+ * callback
+ */
+ *out = vfs_get_link(backing_path.dentry, callback);
+
+ path_put(&backing_path);
+ return 0;
+}
+
+static int fuse_get_link_finalize(struct bpf_fuse_args *fa, const char **out,
+ struct inode *inode, struct dentry *dentry,
+ struct delayed_call *callback)
+{
+ return 0;
+}
+
+int fuse_bpf_get_link(const char **out, struct inode *inode, struct dentry *dentry,
+ struct delayed_call *callback)
+{
+ return bpf_fuse_backing(inode, struct fuse_get_link_args, out,
+ fuse_get_link_initialize_in, fuse_get_link_initialize_out,
+ fuse_get_link_backing, fuse_get_link_finalize,
+ inode, dentry, callback);
+}
+
+struct fuse_symlink_args {
+ struct fuse_buffer name;
+ struct fuse_buffer path;
+};
+
+static int fuse_symlink_initialize_in(struct bpf_fuse_args *fa, struct fuse_symlink_args *args,
+ struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+ *args = (struct fuse_symlink_args) {
+ .name = (struct fuse_buffer) {
+ .data = (void *) entry->d_name.name,
+ .size = entry->d_name.len + 1,
+ .flags = BPF_FUSE_IMMUTABLE,
+ },
+ .path = (struct fuse_buffer) {
+ .data = (void *) link,
+ .size = len,
+ .max_size = PATH_MAX,
+ .flags = BPF_FUSE_VARIABLE_SIZE | BPF_FUSE_MUST_ALLOCATE,
+ },
+ };
+ *fa = (struct bpf_fuse_args) {
+ .info = (struct bpf_fuse_meta_info) {
+ .nodeid = get_node_id(dir),
+ .opcode = FUSE_SYMLINK,
+ },
+ .in_numargs = 2,
+ .in_args[0] = (struct bpf_fuse_arg) {
+ .is_buffer = true,
+ .buffer = &args->name,
+ },
+ .in_args[1] = (struct bpf_fuse_arg) {
+ .is_buffer = true,
+ .buffer = &args->path,
+ },
+ };
+
+ return 0;
+}
+
+static int fuse_symlink_initialize_out(struct bpf_fuse_args *fa, struct fuse_symlink_args *args,
+ struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+ return 0;
+}
+
+static int fuse_symlink_backing(struct bpf_fuse_args *fa, int *out,
+ struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+ struct fuse_inode *fuse_inode = get_fuse_inode(dir);
+ struct inode *backing_inode = fuse_inode->backing_inode;
+ struct path backing_path;
+ struct inode *inode = NULL;
+
+ *out = 0;
+ //TODO Actually deal with changing the backing entry in symlink
+ get_fuse_backing_path(entry, &backing_path);
+ if (!backing_path.dentry)
+ return -EBADF;
+
+ inode_lock_nested(backing_inode, I_MUTEX_PARENT);
+ *out = vfs_symlink(&nop_mnt_idmap, backing_inode, backing_path.dentry,
+ link);
+ inode_unlock(backing_inode);
+ if (*out)
+ goto out;
+ if (d_really_is_negative(backing_path.dentry) ||
+ unlikely(d_unhashed(backing_path.dentry))) {
+ *out = -EINVAL;
+ /**
+ * TODO: overlayfs responds to this situation with a
+ * lookupOneLen. Should we do that too?
+ */
+ goto out;
+ }
+ inode = fuse_iget_backing(dir->i_sb, fuse_inode->nodeid, backing_inode);
+ if (IS_ERR(inode)) {
+ *out = PTR_ERR(inode);
+ goto out;
+ }
+ d_instantiate(entry, inode);
+out:
+ path_put(&backing_path);
+ return *out;
+}
+
+static int fuse_symlink_finalize(struct bpf_fuse_args *fa, int *out,
+ struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+ return 0;
+}
+
+int fuse_bpf_symlink(int *out, struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+ return bpf_fuse_backing(dir, struct fuse_symlink_args, out,
+ fuse_symlink_initialize_in, fuse_symlink_initialize_out,
+ fuse_symlink_backing, fuse_symlink_finalize,
+ dir, entry, link, len);
+}
+
struct fuse_read_args {
struct fuse_read_in in;
struct fuse_read_out out;
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 77d231ab1d9c..08f93a981665 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1033,6 +1033,10 @@ static int fuse_symlink(struct mnt_idmap *idmap, struct inode *dir,
struct fuse_mount *fm = get_fuse_mount(dir);
unsigned len = strlen(link) + 1;
FUSE_ARGS(args);
+ int err;
+
+ if (fuse_bpf_symlink(&err, dir, entry, link, len))
+ return err;

args.opcode = FUSE_SYMLINK;
args.in_numargs = 2;
@@ -1239,6 +1243,9 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
struct fuse_mount *fm = get_fuse_mount(inode);
FUSE_ARGS(args);

+ if (fuse_bpf_link(&err, inode, entry, newdir, newent))
+ return err;
+
memset(&inarg, 0, sizeof(inarg));
inarg.oldnodeid = get_node_id(inode);
args.opcode = FUSE_LINK;
@@ -1741,12 +1748,16 @@ static const char *fuse_get_link(struct dentry *dentry, struct inode *inode,
{
struct fuse_conn *fc = get_fuse_conn(inode);
struct page *page;
+ const char *out = NULL;
int err;

err = -EIO;
if (fuse_is_bad(inode))
goto out_err;

+ if (fuse_bpf_get_link(&out, inode, dentry, callback))
+ return out;
+
if (fc->cache_symlinks)
return page_get_link(dentry, inode, callback);

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 127758575ddc..8ae6ad967f95 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1450,6 +1450,7 @@ int fuse_bpf_rename2(int *out, struct inode *olddir, struct dentry *oldent,
int fuse_bpf_rename(int *out, struct inode *olddir, struct dentry *oldent,
struct inode *newdir, struct dentry *newent);
int fuse_bpf_unlink(int *out, struct inode *dir, struct dentry *entry);
+int fuse_bpf_link(int *out, struct inode *inode, struct dentry *entry, struct inode *dir, struct dentry *newent);
int fuse_bpf_release(int *out, struct inode *inode, struct fuse_file *ff);
int fuse_bpf_releasedir(int *out, struct inode *inode, struct fuse_file *ff);
int fuse_bpf_flush(int *out, struct inode *inode, struct file *file, fl_owner_t id);
@@ -1474,6 +1475,9 @@ int fuse_bpf_getattr(int *out, struct inode *inode, const struct dentry *entry,
u32 request_mask, unsigned int flags);
int fuse_bpf_setattr(int *out, struct inode *inode, struct dentry *dentry, struct iattr *attr, struct file *file);
int fuse_bpf_statfs(int *out, struct inode *inode, struct dentry *dentry, struct kstatfs *buf);
+int fuse_bpf_get_link(const char **out, struct inode *inode, struct dentry *dentry,
+ struct delayed_call *callback);
+int fuse_bpf_symlink(int *out, struct inode *dir, struct dentry *entry, const char *link, int len);
int fuse_bpf_readdir(int *out, struct inode *inode, struct file *file, struct dir_context *ctx);
int fuse_bpf_access(int *out, struct inode *inode, int mask);

@@ -1523,6 +1527,11 @@ static inline int fuse_bpf_unlink(int *out, struct inode *dir, struct dentry *en
return 0;
}

+static inline int fuse_bpf_link(int *out, struct inode *inode, struct dentry *entry, struct inode *dir, struct dentry *newent)
+{
+ return 0;
+}
+
static inline int fuse_bpf_release(int *out, struct inode *inode, struct file *file)
{
return 0;
@@ -1619,6 +1628,17 @@ static inline int fuse_bpf_statfs(int *out, struct inode *inode, struct dentry *
return 0;
}

+static inline int fuse_bpf_get_link(const char **out, struct inode *inode, struct dentry *dentry,
+ struct delayed_call *callback)
+{
+ return 0;
+}
+
+static inline int fuse_bpf_symlink(int *out, struct inode *dir, struct dentry *entry, const char *link, int len)
+{
+ return 0;
+}
+
static inline int fuse_bpf_readdir(int *out, struct inode *inode, struct file *file, struct dir_context *ctx)
{
return 0;
--
2.44.0.478.gd926399ef9-goog