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Subject[PATCH v3 47/68] cachefiles: Implement culling daemon commands
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Implement the ability for the userspace daemon to try and cull a file or
directory in the cache. Two daemon commands are implemented:

(1) The "inuse" command. This queries if a file is in use or whether it
can be deleted. It checks the S_KERNEL_FILE flag on the inode
referred to by the specified filename.

(2) The "cull" command. This asks for a file or directory to be removed,
where removal means either unlinking it or moving it to the graveyard
directory for userspace to dismantle.

Changes
=======
ver #2:
- Fix logging of wrong error[1].
- Need to unmark an inode we've moved to the graveyard before unlocking.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/20211203094950.GA2480@kili/ [1]
Link: https://lore.kernel.org/r/163819643179.215744.13641580295708315695.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906945705.143852.8177595531814485350.stgit@warthog.procyon.org.uk/ # v2
---

fs/cachefiles/daemon.c | 4 -
fs/cachefiles/internal.h | 11 ++
fs/cachefiles/namei.c | 307 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 320 insertions(+), 2 deletions(-)

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 337597a4e30c..985c3f3e6767 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -574,7 +574,7 @@ static int cachefiles_daemon_cull(struct cachefiles_cache *cache, char *args)
goto notdir;

cachefiles_begin_secure(cache, &saved_cred);
- ret = -ENOANO; // PLACEHOLDER: Do culling
+ ret = cachefiles_cull(cache, path.dentry, args);
cachefiles_end_secure(cache, saved_cred);

path_put(&path);
@@ -645,7 +645,7 @@ static int cachefiles_daemon_inuse(struct cachefiles_cache *cache, char *args)
goto notdir;

cachefiles_begin_secure(cache, &saved_cred);
- ret = -ENOANO; // PLACEHOLDER: Check if in use
+ ret = cachefiles_check_in_use(cache, path.dentry, args);
cachefiles_end_secure(cache, saved_cred);

path_put(&path);
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index 7c67a70a3dff..654dbd51b965 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -189,12 +189,23 @@ extern struct kmem_cache *cachefiles_object_jar;
*/
extern void cachefiles_unmark_inode_in_use(struct cachefiles_object *object,
struct file *file);
+extern int cachefiles_bury_object(struct cachefiles_cache *cache,
+ struct cachefiles_object *object,
+ struct dentry *dir,
+ struct dentry *rep,
+ enum fscache_why_object_killed why);
extern struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
struct dentry *dir,
const char *name,
bool *_is_new);
extern void cachefiles_put_directory(struct dentry *dir);

+extern int cachefiles_cull(struct cachefiles_cache *cache, struct dentry *dir,
+ char *filename);
+
+extern int cachefiles_check_in_use(struct cachefiles_cache *cache,
+ struct dentry *dir, char *filename);
+
/*
* security.c
*/
diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index db60a671c3fc..e87c401239f1 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -217,3 +217,310 @@ void cachefiles_put_directory(struct dentry *dir)
dput(dir);
}
}
+
+/*
+ * Remove a regular file from the cache.
+ */
+static int cachefiles_unlink(struct cachefiles_cache *cache,
+ struct cachefiles_object *object,
+ struct dentry *dir, struct dentry *dentry,
+ enum fscache_why_object_killed why)
+{
+ struct path path = {
+ .mnt = cache->mnt,
+ .dentry = dir,
+ };
+ int ret;
+
+ trace_cachefiles_unlink(object, dentry, why);
+ ret = security_path_unlink(&path, dentry);
+ if (ret < 0) {
+ cachefiles_io_error(cache, "Unlink security error");
+ return ret;
+ }
+
+ ret = cachefiles_inject_remove_error();
+ if (ret == 0) {
+ ret = vfs_unlink(&init_user_ns, d_backing_inode(dir), dentry, NULL);
+ if (ret == -EIO)
+ cachefiles_io_error(cache, "Unlink failed");
+ }
+ if (ret != 0)
+ trace_cachefiles_vfs_error(object, d_backing_inode(dir), ret,
+ cachefiles_trace_unlink_error);
+ return ret;
+}
+
+/*
+ * Delete an object representation from the cache
+ * - File backed objects are unlinked
+ * - Directory backed objects are stuffed into the graveyard for userspace to
+ * delete
+ */
+int cachefiles_bury_object(struct cachefiles_cache *cache,
+ struct cachefiles_object *object,
+ struct dentry *dir,
+ struct dentry *rep,
+ enum fscache_why_object_killed why)
+{
+ struct dentry *grave, *trap;
+ struct path path, path_to_graveyard;
+ char nbuffer[8 + 8 + 1];
+ int ret;
+
+ _enter(",'%pd','%pd'", dir, rep);
+
+ if (rep->d_parent != dir) {
+ inode_unlock(d_inode(dir));
+ _leave(" = -ESTALE");
+ return -ESTALE;
+ }
+
+ /* non-directories can just be unlinked */
+ if (!d_is_dir(rep)) {
+ dget(rep); /* Stop the dentry being negated if it's only pinned
+ * by a file struct.
+ */
+ ret = cachefiles_unlink(cache, object, dir, rep, why);
+ dput(rep);
+
+ inode_unlock(d_inode(dir));
+ _leave(" = %d", ret);
+ return ret;
+ }
+
+ /* directories have to be moved to the graveyard */
+ _debug("move stale object to graveyard");
+ inode_unlock(d_inode(dir));
+
+try_again:
+ /* first step is to make up a grave dentry in the graveyard */
+ sprintf(nbuffer, "%08x%08x",
+ (uint32_t) ktime_get_real_seconds(),
+ (uint32_t) atomic_inc_return(&cache->gravecounter));
+
+ /* do the multiway lock magic */
+ trap = lock_rename(cache->graveyard, dir);
+
+ /* do some checks before getting the grave dentry */
+ if (rep->d_parent != dir || IS_DEADDIR(d_inode(rep))) {
+ /* the entry was probably culled when we dropped the parent dir
+ * lock */
+ unlock_rename(cache->graveyard, dir);
+ _leave(" = 0 [culled?]");
+ return 0;
+ }
+
+ if (!d_can_lookup(cache->graveyard)) {
+ unlock_rename(cache->graveyard, dir);
+ cachefiles_io_error(cache, "Graveyard no longer a directory");
+ return -EIO;
+ }
+
+ if (trap == rep) {
+ unlock_rename(cache->graveyard, dir);
+ cachefiles_io_error(cache, "May not make directory loop");
+ return -EIO;
+ }
+
+ if (d_mountpoint(rep)) {
+ unlock_rename(cache->graveyard, dir);
+ cachefiles_io_error(cache, "Mountpoint in cache");
+ return -EIO;
+ }
+
+ grave = lookup_one_len(nbuffer, cache->graveyard, strlen(nbuffer));
+ if (IS_ERR(grave)) {
+ unlock_rename(cache->graveyard, dir);
+ trace_cachefiles_vfs_error(object, d_inode(cache->graveyard),
+ PTR_ERR(grave),
+ cachefiles_trace_lookup_error);
+
+ if (PTR_ERR(grave) == -ENOMEM) {
+ _leave(" = -ENOMEM");
+ return -ENOMEM;
+ }
+
+ cachefiles_io_error(cache, "Lookup error %ld", PTR_ERR(grave));
+ return -EIO;
+ }
+
+ if (d_is_positive(grave)) {
+ unlock_rename(cache->graveyard, dir);
+ dput(grave);
+ grave = NULL;
+ cond_resched();
+ goto try_again;
+ }
+
+ if (d_mountpoint(grave)) {
+ unlock_rename(cache->graveyard, dir);
+ dput(grave);
+ cachefiles_io_error(cache, "Mountpoint in graveyard");
+ return -EIO;
+ }
+
+ /* target should not be an ancestor of source */
+ if (trap == grave) {
+ unlock_rename(cache->graveyard, dir);
+ dput(grave);
+ cachefiles_io_error(cache, "May not make directory loop");
+ return -EIO;
+ }
+
+ /* attempt the rename */
+ path.mnt = cache->mnt;
+ path.dentry = dir;
+ path_to_graveyard.mnt = cache->mnt;
+ path_to_graveyard.dentry = cache->graveyard;
+ ret = security_path_rename(&path, rep, &path_to_graveyard, grave, 0);
+ if (ret < 0) {
+ cachefiles_io_error(cache, "Rename security error %d", ret);
+ } else {
+ struct renamedata rd = {
+ .old_mnt_userns = &init_user_ns,
+ .old_dir = d_inode(dir),
+ .old_dentry = rep,
+ .new_mnt_userns = &init_user_ns,
+ .new_dir = d_inode(cache->graveyard),
+ .new_dentry = grave,
+ };
+ trace_cachefiles_rename(object, rep, grave, why);
+ ret = cachefiles_inject_read_error();
+ if (ret == 0)
+ ret = vfs_rename(&rd);
+ if (ret != 0)
+ trace_cachefiles_vfs_error(object, d_inode(dir), ret,
+ cachefiles_trace_rename_error);
+ if (ret != 0 && ret != -ENOMEM)
+ cachefiles_io_error(cache,
+ "Rename failed with error %d", ret);
+ }
+
+ __cachefiles_unmark_inode_in_use(object, rep);
+ unlock_rename(cache->graveyard, dir);
+ dput(grave);
+ _leave(" = 0");
+ return 0;
+}
+
+/*
+ * Look up an inode to be checked or culled. Return -EBUSY if the inode is
+ * marked in use.
+ */
+static struct dentry *cachefiles_lookup_for_cull(struct cachefiles_cache *cache,
+ struct dentry *dir,
+ char *filename)
+{
+ struct dentry *victim;
+ int ret = -ENOENT;
+
+ inode_lock_nested(d_inode(dir), I_MUTEX_PARENT);
+
+ victim = lookup_one_len(filename, dir, strlen(filename));
+ if (IS_ERR(victim))
+ goto lookup_error;
+ if (d_is_negative(victim))
+ goto lookup_put;
+ if (d_inode(victim)->i_flags & S_KERNEL_FILE)
+ goto lookup_busy;
+ return victim;
+
+lookup_busy:
+ ret = -EBUSY;
+lookup_put:
+ inode_unlock(d_inode(dir));
+ dput(victim);
+ return ERR_PTR(ret);
+
+lookup_error:
+ inode_unlock(d_inode(dir));
+ ret = PTR_ERR(victim);
+ if (ret == -ENOENT)
+ return ERR_PTR(-ESTALE); /* Probably got retired by the netfs */
+
+ if (ret == -EIO) {
+ cachefiles_io_error(cache, "Lookup failed");
+ } else if (ret != -ENOMEM) {
+ pr_err("Internal error: %d\n", ret);
+ ret = -EIO;
+ }
+
+ return ERR_PTR(ret);
+}
+
+/*
+ * Cull an object if it's not in use
+ * - called only by cache manager daemon
+ */
+int cachefiles_cull(struct cachefiles_cache *cache, struct dentry *dir,
+ char *filename)
+{
+ struct dentry *victim;
+ struct inode *inode;
+ int ret;
+
+ _enter(",%pd/,%s", dir, filename);
+
+ victim = cachefiles_lookup_for_cull(cache, dir, filename);
+ if (IS_ERR(victim))
+ return PTR_ERR(victim);
+
+ /* check to see if someone is using this object */
+ inode = d_inode(victim);
+ inode_lock(inode);
+ if (inode->i_flags & S_KERNEL_FILE) {
+ ret = -EBUSY;
+ } else {
+ /* Stop the cache from picking it back up */
+ inode->i_flags |= S_KERNEL_FILE;
+ ret = 0;
+ }
+ inode_unlock(inode);
+ if (ret < 0)
+ goto error_unlock;
+
+ ret = cachefiles_bury_object(cache, NULL, dir, victim,
+ FSCACHE_OBJECT_WAS_CULLED);
+ if (ret < 0)
+ goto error;
+
+ dput(victim);
+ _leave(" = 0");
+ return 0;
+
+error_unlock:
+ inode_unlock(d_inode(dir));
+error:
+ dput(victim);
+ if (ret == -ENOENT)
+ return -ESTALE; /* Probably got retired by the netfs */
+
+ if (ret != -ENOMEM) {
+ pr_err("Internal error: %d\n", ret);
+ ret = -EIO;
+ }
+
+ _leave(" = %d", ret);
+ return ret;
+}
+
+/*
+ * Find out if an object is in use or not
+ * - called only by cache manager daemon
+ * - returns -EBUSY or 0 to indicate whether an object is in use or not
+ */
+int cachefiles_check_in_use(struct cachefiles_cache *cache, struct dentry *dir,
+ char *filename)
+{
+ struct dentry *victim;
+ int ret = 0;
+
+ victim = cachefiles_lookup_for_cull(cache, dir, filename);
+ if (IS_ERR(victim))
+ return PTR_ERR(victim);
+
+ inode_unlock(d_inode(dir));
+ dput(victim);
+ return ret;
+}

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