[RFC Aufs2 #2 14/28] aufs pseudo-link

["J. R. Okajima" <hooanon05@yahoo.co.jp>]

initial commit
pseudo-link is a logical hardlink over branches or different filesystems.

Signed-off-by: J. R. Okajima <hooanon05@yahoo.co.jp>
---
 fs/aufs/plink.c |  335 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 335 insertions(+), 0 deletions(-)
 create mode 100644 fs/aufs/plink.c

diff --git a/fs/aufs/plink.c b/fs/aufs/plink.c
new file mode 100644
index 0000000..62d258f
--- /dev/null
+++ b/fs/aufs/plink.c
@@ -0,0 +1,335 @@
+/*
+ * Copyright (C) 2005-2009 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+/*
+ * pseudo-link
+ */
+
+#include "aufs.h"
+
+/*
+ * during a user process maintains the pseudo-links,
+ * prohibit adding a new plink and branch manipulation.
+ */
+void au_plink_block_maintain(struct super_block *sb)
+{
+	struct au_sbinfo *sbi = au_sbi(sb);
+	/* gave up wake_up_bit() */
+	wait_event(sbi->si_plink_wq, !au_ftest_si(sbi, MAINTAIN_PLINK));
+}
+
+/* ---------------------------------------------------------------------- */
+
+struct pseudo_link {
+	struct list_head list;
+	struct inode *inode;
+};
+
+#ifdef CONFIG_AUFS_DEBUG
+void au_plink_list(struct super_block *sb)
+{
+	struct au_sbinfo *sbinfo;
+	struct list_head *plink_list;
+	struct pseudo_link *plink;
+
+	sbinfo = au_sbi(sb);
+	AuDebugOn(!au_opt_test(au_mntflags(sb), PLINK));
+
+	plink_list = &sbinfo->si_plink.head;
+	spin_lock(&sbinfo->si_plink.spin);
+	list_for_each_entry(plink, plink_list, list)
+		AuDbg("%lu\n", plink->inode->i_ino);
+	spin_unlock(&sbinfo->si_plink.spin);
+}
+#endif
+
+/* is the inode pseudo-linked? */
+int au_plink_test(struct inode *inode)
+{
+	int found;
+	struct au_sbinfo *sbinfo;
+	struct list_head *plink_list;
+	struct pseudo_link *plink;
+
+	sbinfo = au_sbi(inode->i_sb);
+	AuDebugOn(!au_opt_test(au_mntflags(inode->i_sb), PLINK));
+
+	found = 0;
+	plink_list = &sbinfo->si_plink.head;
+	spin_lock(&sbinfo->si_plink.spin);
+	list_for_each_entry(plink, plink_list, list)
+		if (plink->inode == inode) {
+			found = 1;
+			break;
+		}
+	spin_unlock(&sbinfo->si_plink.spin);
+	return found;
+}
+
+/* ---------------------------------------------------------------------- */
+
+/*
+ * generate a name for plink.
+ * the file will be stored under AUFS_WH_PLINKDIR.
+ */
+/* 20 is max digits length of ulong 64 */
+#define PLINK_NAME_LEN	((20 + 1) * 2)
+
+static int plink_name(char *name, int len, struct inode *inode,
+		      aufs_bindex_t bindex)
+{
+	int rlen;
+	struct inode *h_inode;
+
+	h_inode = au_h_iptr(inode, bindex);
+	rlen = snprintf(name, len, "%lu.%lu", inode->i_ino, h_inode->i_ino);
+	return rlen;
+}
+
+/* lookup the plink-ed @inode under the branch at @bindex */
+struct dentry *au_plink_lkup(struct inode *inode, aufs_bindex_t bindex)
+{
+	struct dentry *h_dentry, *h_parent;
+	struct au_branch *br;
+	struct inode *h_dir;
+	char a[PLINK_NAME_LEN];
+	struct qstr tgtname = {
+		.name	= a
+	};
+
+	br = au_sbr(inode->i_sb, bindex);
+	h_parent = br->br_wbr->wbr_plink;
+	h_dir = h_parent->d_inode;
+	tgtname.len = plink_name(a, sizeof(a), inode, bindex);
+
+	/* always superio. */
+	mutex_lock_nested(&h_dir->i_mutex, AuLsc_I_CHILD2);
+	h_dentry = au_sio_lkup_one(&tgtname, h_parent, br);
+	mutex_unlock(&h_dir->i_mutex);
+	return h_dentry;
+}
+
+/* create a pseudo-link */
+static int do_whplink(struct qstr *tgt, struct dentry *h_parent,
+		      struct dentry *h_dentry, struct au_branch *br)
+{
+	int err;
+	struct path h_path = {
+		.mnt = br->br_mnt
+	};
+	struct inode *h_dir;
+
+	h_dir = h_parent->d_inode;
+ again:
+	h_path.dentry = au_lkup_one(tgt, h_parent, br, /*nd*/NULL);
+	err = PTR_ERR(h_path.dentry);
+	if (IS_ERR(h_path.dentry))
+		goto out;
+
+	err = 0;
+	/* wh.plink dir is not monitored */
+	if (h_path.dentry->d_inode
+	    && h_path.dentry->d_inode != h_dentry->d_inode) {
+		err = vfsub_unlink(h_dir, &h_path, /*force*/0);
+		dput(h_path.dentry);
+		h_path.dentry = NULL;
+		if (!err)
+			goto again;
+	}
+	if (!err && !h_path.dentry->d_inode)
+		err = vfsub_link(h_dentry, h_dir, &h_path);
+	dput(h_path.dentry);
+
+ out:
+	return err;
+}
+
+struct do_whplink_args {
+	int *errp;
+	struct qstr *tgt;
+	struct dentry *h_parent;
+	struct dentry *h_dentry;
+	struct au_branch *br;
+};
+
+static void call_do_whplink(void *args)
+{
+	struct do_whplink_args *a = args;
+	*a->errp = do_whplink(a->tgt, a->h_parent, a->h_dentry, a->br);
+}
+
+static int whplink(struct dentry *h_dentry, struct inode *inode,
+		   aufs_bindex_t bindex, struct au_branch *br)
+{
+	int err, wkq_err;
+	struct au_wbr *wbr;
+	struct dentry *h_parent;
+	struct inode *h_dir;
+	char a[PLINK_NAME_LEN];
+	struct qstr tgtname = {
+		.name = a
+	};
+
+	wbr = au_sbr(inode->i_sb, bindex)->br_wbr;
+	h_parent = wbr->wbr_plink;
+	h_dir = h_parent->d_inode;
+	tgtname.len = plink_name(a, sizeof(a), inode, bindex);
+
+	/* always superio. */
+	mutex_lock_nested(&h_dir->i_mutex, AuLsc_I_CHILD2);
+	if (!au_test_wkq(current)) {
+		struct do_whplink_args args = {
+			.errp		= &err,
+			.tgt		= &tgtname,
+			.h_parent	= h_parent,
+			.h_dentry	= h_dentry,
+			.br		= br
+		};
+		wkq_err = au_wkq_wait(call_do_whplink, &args);
+		if (unlikely(wkq_err))
+			err = wkq_err;
+	} else
+		err = do_whplink(&tgtname, h_parent, h_dentry, br);
+	mutex_unlock(&h_dir->i_mutex);
+
+	return err;
+}
+
+/* free a single plink */
+static void do_put_plink(struct pseudo_link *plink, int do_del)
+{
+	iput(plink->inode);
+	if (do_del)
+		list_del(&plink->list);
+	kfree(plink);
+}
+
+/*
+ * create a new pseudo-link for @h_dentry on @bindex.
+ * the linked inode is held in aufs @inode.
+ */
+void au_plink_append(struct inode *inode, aufs_bindex_t bindex,
+		     struct dentry *h_dentry)
+{
+	struct super_block *sb;
+	struct au_sbinfo *sbinfo;
+	struct list_head *plink_list;
+	struct pseudo_link *plink;
+	int found, err, cnt;
+
+	sb = inode->i_sb;
+	sbinfo = au_sbi(sb);
+	AuDebugOn(!au_opt_test(au_mntflags(sb), PLINK));
+
+	err = 0;
+	cnt = 0;
+	found = 0;
+	plink_list = &sbinfo->si_plink.head;
+	spin_lock(&sbinfo->si_plink.spin);
+	list_for_each_entry(plink, plink_list, list) {
+		cnt++;
+		if (plink->inode == inode) {
+			found = 1;
+			break;
+		}
+	}
+	if (found) {
+		spin_unlock(&sbinfo->si_plink.spin);
+		return;
+	}
+
+	plink = NULL;
+	if (!found) {
+		plink = kmalloc(sizeof(*plink), GFP_ATOMIC);
+		if (plink) {
+			plink->inode = au_igrab(inode);
+			list_add(&plink->list, plink_list);
+			cnt++;
+		} else
+			err = -ENOMEM;
+	}
+	spin_unlock(&sbinfo->si_plink.spin);
+
+	if (!err) {
+		au_plink_block_maintain(sb);
+		err = whplink(h_dentry, inode, bindex, au_sbr(sb, bindex));
+	}
+
+	if (unlikely(cnt > AUFS_PLINK_WARN))
+		AuWarn1("unexpectedly many pseudo links, %d\n", cnt);
+	if (unlikely(err)) {
+		AuWarn("err %d, damaged pseudo link.\n", err);
+		if (!found && plink)
+			do_put_plink(plink, /*do_del*/1);
+	}
+}
+
+/* free all plinks */
+void au_plink_put(struct super_block *sb)
+{
+	struct au_sbinfo *sbinfo;
+	struct list_head *plink_list;
+	struct pseudo_link *plink, *tmp;
+
+	sbinfo = au_sbi(sb);
+	AuDebugOn(!au_opt_test(au_mntflags(sb), PLINK));
+
+	plink_list = &sbinfo->si_plink.head;
+	/* no spin_lock since sbinfo is write-locked */
+	list_for_each_entry_safe(plink, tmp, plink_list, list)
+		do_put_plink(plink, 0);
+	INIT_LIST_HEAD(plink_list);
+}
+
+/* free the plinks on a branch specified by @br_id */
+void au_plink_half_refresh(struct super_block *sb, aufs_bindex_t br_id)
+{
+	struct au_sbinfo *sbinfo;
+	struct list_head *plink_list;
+	struct pseudo_link *plink, *tmp;
+	struct inode *inode;
+	aufs_bindex_t bstart, bend, bindex;
+	unsigned char do_put;
+
+	sbinfo = au_sbi(sb);
+	AuDebugOn(!au_opt_test(au_mntflags(sb), PLINK));
+
+	plink_list = &sbinfo->si_plink.head;
+	/* no spin_lock since sbinfo is write-locked */
+	list_for_each_entry_safe(plink, tmp, plink_list, list) {
+		do_put = 0;
+		inode = au_igrab(plink->inode);
+		ii_write_lock_child(inode);
+		bstart = au_ibstart(inode);
+		bend = au_ibend(inode);
+		if (bstart >= 0) {
+			for (bindex = bstart; bindex <= bend; bindex++) {
+				if (!au_h_iptr(inode, bindex)
+				    || au_ii_br_id(inode, bindex) != br_id)
+					continue;
+				au_set_h_iptr(inode, bindex, NULL, 0);
+				do_put = 1;
+				break;
+			}
+		} else
+			do_put_plink(plink, 1);
+
+		if (do_put) {
+			for (bindex = bstart; bindex <= bend; bindex++)
+				if (au_h_iptr(inode, bindex)) {
+					do_put = 0;
+					break;
+				}
+			if (do_put)
+				do_put_plink(plink, 1);
+		}
+		ii_write_unlock(inode);
+		iput(inode);
+	}
+}
-- 
1.6.1.284.g5dc13