[PATCH 8/17] [LogFS] inode.c

[Joern Engel <joern@logfs.org>]

---
 fs/logfs/inode.c                    |  417 +++++++

diff --git a/fs/logfs/inode.c b/fs/logfs/inode.c
new file mode 100644
index 0000000..6d08b37
--- /dev/null
+++ b/fs/logfs/inode.c
@@ -0,0 +1,417 @@
+/*
+ * fs/logfs/inode.c	- inode handling code
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
+ */
+#include "logfs.h"
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+
+/*
+ * How soon to reuse old inode numbers?  LogFS doesn't store deleted inodes
+ * on the medium.  It therefore also lacks a method to store the previous
+ * generation number for deleted inodes.  Instead a single generation number
+ * is stored which will be used for new inodes.  Being just a 32bit counter,
+ * this can obvious wrap relatively quickly.  So we only reuse inodes if we
+ * know that a fair number of inodes can be created before we have to increment
+ * the generation again - effectively adding some bits to the counter.
+ * But being too aggressive here means we keep a very large and very sparse
+ * inode file, wasting space on indirect blocks.
+ * So what is a good value?  Beats me.  64k seems moderately bad on both
+ * fronts, so let's use that for now...
+ *
+ * NFS sucks, as everyone already knows.
+ */
+#define INOS_PER_WRAP (0x10000)
+
+/*
+ * Logfs' requirement to read inodes for garbage collection makes life a bit
+ * harder.  GC may have to read inodes that are in I_FREEING state, when they
+ * are being written out - and waiting for GC to make progress, naturally.
+ *
+ * So we cannot just call iget() or some variant of it, but first have to check
+ * wether the inode in question might be in I_FREEING state.  Therefore we
+ * maintain our own per-sb list of "almost deleted" inodes and check against
+ * that list first.  Normally this should be at most 1-2 entries long.
+ *
+ * Also, inodes have logfs-specific reference counting on top of what the vfs
+ * does.  When .destroy_inode is called, normally the reference count will drop
+ * to zero and the inode gets deleted.  But if GC accessed the inode, its
+ * refcount will remain nonzero and final deletion will have to wait.
+ *
+ * As a result we have two sets of functions to get/put inodes:
+ * logfs_safe_iget/logfs_safe_iput	- safe to call from GC context
+ * logfs_iget/iput			- normal version
+ */
+static struct kmem_cache *logfs_inode_cache;
+
+static DEFINE_SPINLOCK(logfs_inode_lock);
+
+static void logfs_inode_setops(struct inode *inode)
+{
+	switch (inode->i_mode & S_IFMT) {
+	case S_IFDIR:
+		inode->i_op = &logfs_dir_iops;
+		inode->i_fop = &logfs_dir_fops;
+		inode->i_mapping->a_ops = &logfs_reg_aops;
+		break;
+	case S_IFREG:
+		inode->i_op = &logfs_reg_iops;
+		inode->i_fop = &logfs_reg_fops;
+		inode->i_mapping->a_ops = &logfs_reg_aops;
+		break;
+	case S_IFLNK:
+		inode->i_op = &logfs_symlink_iops;
+		inode->i_mapping->a_ops = &logfs_reg_aops;
+		break;
+	case S_IFSOCK:	/* fall through */
+	case S_IFBLK:	/* fall through */
+	case S_IFCHR:	/* fall through */
+	case S_IFIFO:
+		init_special_inode(inode, inode->i_mode, inode->i_rdev);
+		break;
+	default:
+		BUG();
+	}
+}
+
+static struct inode *__logfs_iget(struct super_block *sb, ino_t ino)
+{
+	struct inode *inode = iget_locked(sb, ino);
+	int err;
+
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+	if (!(inode->i_state & I_NEW))
+		return inode;
+
+	err = logfs_read_inode(inode);
+	if (err || inode->i_nlink == 0) {
+		/* inode->i_nlink == 0 can be true when called from
+		 * block validator */
+		/* set i_nlink to 0 to prevent caching */
+		inode->i_nlink = 0;
+		logfs_inode(inode)->li_flags |= LOGFS_IF_ZOMBIE;
+		iget_failed(inode);
+		if (!err)
+			err = -ENOENT;
+		return ERR_PTR(err);
+	}
+
+	logfs_inode_setops(inode);
+	unlock_new_inode(inode);
+	return inode;
+}
+
+struct inode *logfs_iget(struct super_block *sb, ino_t ino)
+{
+	BUG_ON(ino == LOGFS_INO_MASTER);
+	BUG_ON(ino == LOGFS_INO_SEGFILE);
+	return __logfs_iget(sb, ino);
+}
+
+/*
+ * is_cached is set to 1 if we hand out a cached inode, 0 otherwise.
+ * this allows logfs_iput to do the right thing later
+ */
+struct inode *logfs_safe_iget(struct super_block *sb, ino_t ino, int *is_cached)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_inode *li;
+
+	if (ino == LOGFS_INO_MASTER)
+		return super->s_master_inode;
+	if (ino == LOGFS_INO_SEGFILE)
+		return super->s_segfile_inode;
+
+	spin_lock(&logfs_inode_lock);
+	list_for_each_entry(li, &super->s_freeing_list, li_freeing_list)
+		if (li->vfs_inode.i_ino == ino) {
+			li->li_refcount++;
+			spin_unlock(&logfs_inode_lock);
+			*is_cached = 1;
+			return &li->vfs_inode;
+		}
+	spin_unlock(&logfs_inode_lock);
+
+	*is_cached = 0;
+	return __logfs_iget(sb, ino);
+}
+
+static void __logfs_destroy_inode(struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	BUG_ON(li->li_block);
+	list_del(&li->li_freeing_list);
+	kmem_cache_free(logfs_inode_cache, li);
+}
+
+static void logfs_destroy_inode(struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	BUG_ON(list_empty(&li->li_freeing_list));
+	spin_lock(&logfs_inode_lock);
+	li->li_refcount--;
+	if (li->li_refcount == 0)
+		__logfs_destroy_inode(inode);
+	spin_unlock(&logfs_inode_lock);
+}
+
+void logfs_safe_iput(struct inode *inode, int is_cached)
+{
+	if (inode->i_ino == LOGFS_INO_MASTER)
+		return;
+	if (inode->i_ino == LOGFS_INO_SEGFILE)
+		return;
+
+	if (is_cached) {
+		logfs_destroy_inode(inode);
+		return;
+	}
+
+	iput(inode);
+}
+
+static void logfs_init_inode(struct super_block *sb, struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	int i;
+
+	li->li_flags	= 0;
+	li->li_height	= 0;
+	li->li_used_bytes = 0;
+	li->li_block	= NULL;
+	inode->i_uid	= 0;
+	inode->i_gid	= 0;
+	inode->i_size	= 0;
+	inode->i_blocks	= 0;
+	inode->i_ctime	= CURRENT_TIME;
+	inode->i_mtime	= CURRENT_TIME;
+	inode->i_nlink	= 1;
+	INIT_LIST_HEAD(&li->li_freeing_list);
+
+	for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+		li->li_data[i] = 0;
+
+	return;
+}
+
+static struct inode *logfs_alloc_inode(struct super_block *sb)
+{
+	struct logfs_inode *li;
+
+	li = kmem_cache_alloc(logfs_inode_cache, GFP_NOFS);
+	if (!li)
+		return NULL;
+	logfs_init_inode(sb, &li->vfs_inode);
+	return &li->vfs_inode;
+}
+
+/*
+ * In logfs inodes are written to an inode file.  The inode file, like any
+ * other file, is managed with a inode.  The inode file's inode, aka master
+ * inode, requires special handling in several respects.  First, it cannot be
+ * written to the inode file, so it is stored in the journal instead.
+ *
+ * Secondly, this inode cannot be written back and destroyed before all other
+ * inodes have been written.  The ordering is important.  Linux' VFS is happily
+ * unaware of the ordering constraint and would ordinarily destroy the master
+ * inode at umount time while other inodes are still in use and dirty.  Not
+ * good.
+ *
+ * So logfs makes sure the master inode is not written until all other inodes
+ * have been destroyed.  Sadly, this method has another side-effect.  The VFS
+ * will notice one remaining inode and print a frightening warning message.
+ * Worse, it is impossible to judge whether such a warning was caused by the
+ * master inode or any other inodes have leaked as well.
+ *
+ * Our attempt of solving this is with logfs_new_meta_inode() below.  Its
+ * purpose is to create a new inode that will not trigger the warning if such
+ * an inode is still in use.  An ugly hack, no doubt.  Suggections for
+ * improvement are welcome.
+ */
+struct inode *logfs_new_meta_inode(struct super_block *sb, u64 ino)
+{
+	struct inode *inode;
+
+	inode = logfs_alloc_inode(sb);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	inode->i_mode = S_IFREG;
+	inode->i_ino = ino;
+	inode->i_sb = sb;
+
+	/* This is a blatant copy of alloc_inode code.  We'd need alloc_inode
+	 * to be nonstatic, alas. */
+	{
+		struct address_space * const mapping = &inode->i_data;
+
+		mapping->a_ops = &logfs_reg_aops;
+		mapping->host = inode;
+		mapping->flags = 0;
+		mapping_set_gfp_mask(mapping, GFP_NOFS);
+		mapping->assoc_mapping = NULL;
+		mapping->backing_dev_info = &default_backing_dev_info;
+		inode->i_mapping = mapping;
+		inode->i_nlink = 1;
+	}
+
+	return inode;
+}
+
+struct inode *logfs_read_meta_inode(struct super_block *sb, u64 ino)
+{
+	struct inode *inode;
+	int err;
+
+	inode = logfs_new_meta_inode(sb, ino);
+	if (IS_ERR(inode))
+		return inode;
+
+	err = logfs_read_inode(inode);
+	if (err) {
+		destroy_meta_inode(inode);
+		return ERR_PTR(err);
+	}
+	logfs_inode_setops(inode);
+	return inode;
+}
+
+static int logfs_write_inode(struct inode *inode, int do_sync)
+{
+	int ret;
+	long flags = WF_LOCK;
+
+	/* Can only happen if creat() failed.  Safe to skip. */
+	if (logfs_inode(inode)->li_flags & LOGFS_IF_STILLBORN)
+		return 0;
+
+	ret = __logfs_write_inode(inode, flags);
+	LOGFS_BUG_ON(ret, inode->i_sb);
+	return ret;
+}
+
+void destroy_meta_inode(struct inode *inode)
+{
+	if (inode) {
+		if (inode->i_data.nrpages)
+			truncate_inode_pages(&inode->i_data, 0);
+		logfs_clear_inode(inode);
+		kmem_cache_free(logfs_inode_cache, logfs_inode(inode));
+	}
+}
+
+/* called with inode_lock held */
+static void logfs_drop_inode(struct inode *inode)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+	struct logfs_inode *li = logfs_inode(inode);
+
+	spin_lock(&logfs_inode_lock);
+	list_move(&li->li_freeing_list, &super->s_freeing_list);
+	spin_unlock(&logfs_inode_lock);
+	generic_drop_inode(inode);
+}
+
+static void logfs_set_ino_generation(struct super_block *sb,
+		struct inode *inode)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u64 ino;
+
+	mutex_lock(&super->s_journal_mutex);
+	ino = logfs_seek_hole(super->s_master_inode, super->s_last_ino);
+	super->s_last_ino = ino;
+	super->s_inos_till_wrap--;
+	if (super->s_inos_till_wrap < 0) {
+		super->s_last_ino = LOGFS_RESERVED_INOS;
+		super->s_generation++;
+		super->s_inos_till_wrap = INOS_PER_WRAP;
+	}
+	inode->i_ino = ino;
+	inode->i_generation = super->s_generation;
+	mutex_unlock(&super->s_journal_mutex);
+}
+
+struct inode *logfs_new_inode(struct inode *dir, int mode)
+{
+	struct super_block *sb = dir->i_sb;
+	struct inode *inode;
+
+	inode = new_inode(sb);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	logfs_init_inode(sb, inode);
+
+	/* inherit parent flags */
+	logfs_inode(inode)->li_flags |=
+		logfs_inode(dir)->li_flags & LOGFS_FL_INHERITED;
+
+	inode->i_mode = mode;
+	logfs_set_ino_generation(sb, inode);
+
+	inode->i_uid = current_fsuid();
+	inode->i_gid = current_fsgid();
+	if (dir->i_mode & S_ISGID) {
+		inode->i_gid = dir->i_gid;
+		if (S_ISDIR(mode))
+			inode->i_mode |= S_ISGID;
+	}
+
+	logfs_inode_setops(inode);
+	insert_inode_hash(inode);
+
+	return inode;
+}
+
+static void logfs_init_once(void *_li)
+{
+	struct logfs_inode *li = _li;
+	int i;
+
+	li->li_flags = 0;
+	li->li_used_bytes = 0;
+	li->li_refcount = 1;
+	for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+		li->li_data[i] = 0;
+	inode_init_once(&li->vfs_inode);
+}
+
+static int logfs_sync_fs(struct super_block *sb, int wait)
+{
+	/* FIXME: write anchor */
+	logfs_super(sb)->s_devops->sync(sb);
+	return 0;
+}
+
+const struct super_operations logfs_super_operations = {
+	.alloc_inode	= logfs_alloc_inode,
+	.clear_inode	= logfs_clear_inode,
+	.delete_inode	= logfs_delete_inode,
+	.destroy_inode	= logfs_destroy_inode,
+	.drop_inode	= logfs_drop_inode,
+	.write_inode	= logfs_write_inode,
+	.statfs		= logfs_statfs,
+	.sync_fs	= logfs_sync_fs,
+};
+
+int logfs_init_inode_cache(void)
+{
+	logfs_inode_cache = kmem_cache_create("logfs_inode_cache",
+			sizeof(struct logfs_inode), 0, SLAB_RECLAIM_ACCOUNT,
+			logfs_init_once);
+	if (!logfs_inode_cache)
+		return -ENOMEM;
+	return 0;
+}
+
+void logfs_destroy_inode_cache(void)
+{
+	kmem_cache_destroy(logfs_inode_cache);
+}