Re: [PATCH v4 40/68] cachefiles: Implement cache registration and withdrawal

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2021-12-22 at 23:23 +0000, David Howells wrote:
> Do the following:
> 
>  (1) Fill out cachefiles_daemon_add_cache() so that it sets up the cache
>      directories and registers the cache with cachefiles.
> 
>  (2) Add a function to do the top-level part of cache withdrawal and
>      unregistration.
> 
>  (3) Add a function to sync a cache.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: linux-cachefs@redhat.com
> Link: https://lore.kernel.org/r/163819633175.215744.10857127598041268340.stgit@warthog.procyon.org.uk/ # v1
> Link: https://lore.kernel.org/r/163906935445.143852.15545194974036410029.stgit@warthog.procyon.org.uk/ # v2
> Link: https://lore.kernel.org/r/163967142904.1823006.244055483596047072.stgit@warthog.procyon.org.uk/ # v3
> ---
> 
>  fs/cachefiles/Makefile    |    1 
>  fs/cachefiles/cache.c     |  207 +++++++++++++++++++++++++++++++++++++++++++++
>  fs/cachefiles/daemon.c    |    8 +-
>  fs/cachefiles/interface.c |   18 ++++
>  fs/cachefiles/internal.h  |    9 ++
>  5 files changed, 240 insertions(+), 3 deletions(-)
>  create mode 100644 fs/cachefiles/interface.c
> 
> diff --git a/fs/cachefiles/Makefile b/fs/cachefiles/Makefile
> index e0b092ca077f..92af5daee8ce 100644
> --- a/fs/cachefiles/Makefile
> +++ b/fs/cachefiles/Makefile
> @@ -6,6 +6,7 @@
>  cachefiles-y := \
>  	cache.o \
>  	daemon.o \
> +	interface.o \
>  	main.o \
>  	namei.o \
>  	security.o
> diff --git a/fs/cachefiles/cache.c b/fs/cachefiles/cache.c
> index 73636f89eefa..0462e7af87fb 100644
> --- a/fs/cachefiles/cache.c
> +++ b/fs/cachefiles/cache.c
> @@ -10,6 +10,166 @@
>  #include <linux/namei.h>
>  #include "internal.h"
>  
> +/*
> + * Bring a cache online.
> + */
> +int cachefiles_add_cache(struct cachefiles_cache *cache)
> +{
> +	struct fscache_cache *cache_cookie;
> +	struct path path;
> +	struct kstatfs stats;
> +	struct dentry *graveyard, *cachedir, *root;
> +	const struct cred *saved_cred;
> +	int ret;
> +
> +	_enter("");
> +
> +	cache_cookie = fscache_acquire_cache(cache->tag);
> +	if (IS_ERR(cache_cookie))
> +		return PTR_ERR(cache_cookie);
> +
> +	/* we want to work under the module's security ID */
> +	ret = cachefiles_get_security_ID(cache);
> +	if (ret < 0)
> +		goto error_getsec;
> +
> +	cachefiles_begin_secure(cache, &saved_cred);
> +
> +	/* look up the directory at the root of the cache */
> +	ret = kern_path(cache->rootdirname, LOOKUP_DIRECTORY, &path);
> +	if (ret < 0)
> +		goto error_open_root;
> +
> +	cache->mnt = path.mnt;
> +	root = path.dentry;
> +
> +	ret = -EINVAL;
> +	if (mnt_user_ns(path.mnt) != &init_user_ns) {
> +		pr_warn("File cache on idmapped mounts not supported");
> +		goto error_unsupported;
> +	}
> +
> +	/* check parameters */
> +	ret = -EOPNOTSUPP;
> +	if (d_is_negative(root) ||
> +	    !d_backing_inode(root)->i_op->lookup ||
> +	    !d_backing_inode(root)->i_op->mkdir ||
> +	    !(d_backing_inode(root)->i_opflags & IOP_XATTR) ||
> +	    !root->d_sb->s_op->statfs ||
> +	    !root->d_sb->s_op->sync_fs ||
> +	    root->d_sb->s_blocksize > PAGE_SIZE)
> +		goto error_unsupported;
> +

That's quite a collection of tests.

Most are obvious, but some comments explaining the need for others would
not be a bad thing. In particular, why is s_blocksize > PAGE_SIZE
unsupported?

Also, should you vet whether the fs supports i_op->tmpfile here ?

> +	ret = -EROFS;
> +	if (sb_rdonly(root->d_sb))
> +		goto error_unsupported;
> +
> +	/* determine the security of the on-disk cache as this governs
> +	 * security ID of files we create */
> +	ret = cachefiles_determine_cache_security(cache, root, &saved_cred);
> +	if (ret < 0)
> +		goto error_unsupported;
> +
> +	/* get the cache size and blocksize */
> +	ret = vfs_statfs(&path, &stats);
> +	if (ret < 0)
> +		goto error_unsupported;
> +
> +	ret = -ERANGE;
> +	if (stats.f_bsize <= 0)
> +		goto error_unsupported;
> +
> +	ret = -EOPNOTSUPP;
> +	if (stats.f_bsize > PAGE_SIZE)
> +		goto error_unsupported;
> +
> +	cache->bsize = stats.f_bsize;
> +	cache->bshift = 0;
> +	if (stats.f_bsize < PAGE_SIZE)
> +		cache->bshift = PAGE_SHIFT - ilog2(stats.f_bsize);
> +
> +	_debug("blksize %u (shift %u)",
> +	       cache->bsize, cache->bshift);
> +
> +	_debug("size %llu, avail %llu",
> +	       (unsigned long long) stats.f_blocks,
> +	       (unsigned long long) stats.f_bavail);
> +
> +	/* set up caching limits */
> +	do_div(stats.f_files, 100);
> +	cache->fstop = stats.f_files * cache->fstop_percent;
> +	cache->fcull = stats.f_files * cache->fcull_percent;
> +	cache->frun  = stats.f_files * cache->frun_percent;
> +
> +	_debug("limits {%llu,%llu,%llu} files",
> +	       (unsigned long long) cache->frun,
> +	       (unsigned long long) cache->fcull,
> +	       (unsigned long long) cache->fstop);
> +
> +	stats.f_blocks >>= cache->bshift;
> +	do_div(stats.f_blocks, 100);
> +	cache->bstop = stats.f_blocks * cache->bstop_percent;
> +	cache->bcull = stats.f_blocks * cache->bcull_percent;
> +	cache->brun  = stats.f_blocks * cache->brun_percent;
> +
> +	_debug("limits {%llu,%llu,%llu} blocks",
> +	       (unsigned long long) cache->brun,
> +	       (unsigned long long) cache->bcull,
> +	       (unsigned long long) cache->bstop);
> +
> +	/* get the cache directory and check its type */
> +	cachedir = cachefiles_get_directory(cache, root, "cache", NULL);
> +	if (IS_ERR(cachedir)) {
> +		ret = PTR_ERR(cachedir);
> +		goto error_unsupported;
> +	}
> +
> +	cache->store = cachedir;
> +
> +	/* get the graveyard directory */
> +	graveyard = cachefiles_get_directory(cache, root, "graveyard", NULL);
> +	if (IS_ERR(graveyard)) {
> +		ret = PTR_ERR(graveyard);
> +		goto error_unsupported;
> +	}
> +
> +	cache->graveyard = graveyard;
> +	cache->cache = cache_cookie;
> +
> +	ret = fscache_add_cache(cache_cookie, &cachefiles_cache_ops, cache);
> +	if (ret < 0)
> +		goto error_add_cache;
> +
> +	/* done */
> +	set_bit(CACHEFILES_READY, &cache->flags);
> +	dput(root);
> +
> +	pr_info("File cache on %s registered\n", cache_cookie->name);
> +
> +	/* check how much space the cache has */
> +	cachefiles_has_space(cache, 0, 0);
> +	cachefiles_end_secure(cache, saved_cred);
> +	_leave(" = 0 [%px]", cache->cache);
> +	return 0;
> +
> +error_add_cache:
> +	cachefiles_put_directory(cache->graveyard);
> +	cache->graveyard = NULL;
> +error_unsupported:
> +	cachefiles_put_directory(cache->store);
> +	cache->store = NULL;
> +	mntput(cache->mnt);
> +	cache->mnt = NULL;
> +	dput(root);
> +error_open_root:
> +	cachefiles_end_secure(cache, saved_cred);
> +error_getsec:
> +	fscache_relinquish_cache(cache_cookie);
> +	cache->cache = NULL;
> +	pr_err("Failed to register: %d\n", ret);
> +	return ret;
> +}
> +
>  /*
>   * See if we have space for a number of pages and/or a number of files in the
>   * cache
> @@ -101,3 +261,50 @@ int cachefiles_has_space(struct cachefiles_cache *cache,
>  	_leave(" = %d", ret);
>  	return ret;
>  }
> +
> +/*
> + * Sync a cache to backing disk.
> + */
> +static void cachefiles_sync_cache(struct cachefiles_cache *cache)
> +{
> +	const struct cred *saved_cred;
> +	int ret;
> +
> +	_enter("%s", cache->cache->name);
> +
> +	/* make sure all pages pinned by operations on behalf of the netfs are
> +	 * written to disc */
> +	cachefiles_begin_secure(cache, &saved_cred);
> +	down_read(&cache->mnt->mnt_sb->s_umount);
> +	ret = sync_filesystem(cache->mnt->mnt_sb);
> +	up_read(&cache->mnt->mnt_sb->s_umount);
> +	cachefiles_end_secure(cache, saved_cred);
> +
> +	if (ret == -EIO)
> +		cachefiles_io_error(cache,
> +				    "Attempt to sync backing fs superblock returned error %d",
> +				    ret);
> +}
> +
> +/*
> + * Withdraw cache objects.
> + */
> +void cachefiles_withdraw_cache(struct cachefiles_cache *cache)
> +{
> +	struct fscache_cache *fscache = cache->cache;
> +
> +	pr_info("File cache on %s unregistering\n", fscache->name);
> +
> +	fscache_withdraw_cache(fscache);
> +
> +	/* we now have to destroy all the active objects pertaining to this
> +	 * cache - which we do by passing them off to thread pool to be
> +	 * disposed of */
> +	// PLACEHOLDER: Withdraw objects
> +	fscache_wait_for_objects(fscache);
> +
> +	// PLACEHOLDER: Withdraw volume
> +	cachefiles_sync_cache(cache);
> +	cache->cache = NULL;
> +	fscache_relinquish_cache(fscache);
> +}
> diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
> index 7d4691614cec..a449ee661987 100644
> --- a/fs/cachefiles/daemon.c
> +++ b/fs/cachefiles/daemon.c
> @@ -702,6 +702,7 @@ static int cachefiles_daemon_bind(struct cachefiles_cache *cache, char *args)
>  
>  	pr_warn("Cache is disabled for development\n");
>  	return -ENOANO; // Don't allow the cache to operate yet
> +	//return cachefiles_add_cache(cache);
>  }
>  
>  /*
> @@ -711,10 +712,11 @@ static void cachefiles_daemon_unbind(struct cachefiles_cache *cache)
>  {
>  	_enter("");
>  
> -	if (test_bit(CACHEFILES_READY, &cache->flags)) {
> -		// PLACEHOLDER: Withdraw cache
> -	}
> +	if (test_bit(CACHEFILES_READY, &cache->flags))
> +		cachefiles_withdraw_cache(cache);
>  
> +	cachefiles_put_directory(cache->graveyard);
> +	cachefiles_put_directory(cache->store);
>  	mntput(cache->mnt);
>  
>  	kfree(cache->rootdirname);
> diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
> new file mode 100644
> index 000000000000..564ea8fa6641
> --- /dev/null
> +++ b/fs/cachefiles/interface.c
> @@ -0,0 +1,18 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/* FS-Cache interface to CacheFiles
> + *
> + * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + */
> +
> +#include <linux/slab.h>
> +#include <linux/mount.h>
> +#include <linux/xattr.h>
> +#include <linux/file.h>
> +#include <linux/falloc.h>
> +#include <trace/events/fscache.h>
> +#include "internal.h"
> +
> +const struct fscache_cache_ops cachefiles_cache_ops = {
> +	.name			= "cachefiles",
> +};
> diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
> index 48768a3ab105..77e874c2bbe7 100644
> --- a/fs/cachefiles/internal.h
> +++ b/fs/cachefiles/internal.h
> @@ -32,6 +32,8 @@ struct cachefiles_object {
>  struct cachefiles_cache {
>  	struct fscache_cache		*cache;		/* Cache cookie */
>  	struct vfsmount			*mnt;		/* mountpoint holding the cache */
> +	struct dentry			*store;		/* Directory into which live objects go */
> +	struct dentry			*graveyard;	/* directory into which dead objects go */
>  	struct file			*cachefilesd;	/* manager daemon handle */
>  	const struct cred		*cache_cred;	/* security override for accessing cache */
>  	struct mutex			daemon_mutex;	/* command serialisation mutex */
> @@ -78,8 +80,10 @@ static inline void cachefiles_state_changed(struct cachefiles_cache *cache)
>  /*
>   * cache.c
>   */
> +extern int cachefiles_add_cache(struct cachefiles_cache *cache);
>  extern int cachefiles_has_space(struct cachefiles_cache *cache,
>  				unsigned fnr, unsigned bnr);
> +extern void cachefiles_withdraw_cache(struct cachefiles_cache *cache);
>  
>  /*
>   * daemon.c
> @@ -125,6 +129,11 @@ static inline int cachefiles_inject_remove_error(void)
>  	return cachefiles_error_injection_state & 2 ? -EIO : 0;
>  }
>  
> +/*
> + * interface.c
> + */
> +extern const struct fscache_cache_ops cachefiles_cache_ops;
> +
>  /*
>   * namei.c
>   */
> 
> 

-- 
Jeff Layton <jlayton@kernel.org>