JFFS2: Add parameter to reserve disk space for root

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=8da8ba2ea6ad52ea8558384f38586b0c1a516e9d
Commit:     8da8ba2ea6ad52ea8558384f38586b0c1a516e9d
Parent:     886bd33da7cfb1f6c7f3396f7146278ed02e76a7
Author:     Daniel Drake <dsd at laptop.org>
AuthorDate: Tue Apr 10 22:22:35 2012 +0100
Committer:  David Woodhouse <David.Woodhouse at intel.com>
CommitDate: Sun May 13 22:51:29 2012 -0500

    JFFS2: Add parameter to reserve disk space for root
    
    Add a new rp_size= parameter which creates a "reserved pool" of disk
    space which can only be used by root. Other users are not permitted
    to write to disk when the available space is less than the pool size.
    
    Based on original code by Artem Bityutskiy in
    https://dev.laptop.org/ticket/5317
    
    [dwmw2: use capable(CAP_SYS_RESOURCE) not uid/gid check, fix debug prints]
    Signed-off-by: Daniel Drake <dsd at laptop.org>
    Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy at linux.intel.com>
    Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
---
 fs/jffs2/jffs2_fs_sb.h |    7 +++++++
 fs/jffs2/nodemgmt.c    |   42 ++++++++++++++++++++++++++++++++++++++++++
 fs/jffs2/super.c       |   17 +++++++++++++++++
 3 files changed, 66 insertions(+), 0 deletions(-)

diff --git a/fs/jffs2/jffs2_fs_sb.h b/fs/jffs2/jffs2_fs_sb.h
index 55a0c1d..0d00bf2 100644
--- a/fs/jffs2/jffs2_fs_sb.h
+++ b/fs/jffs2/jffs2_fs_sb.h
@@ -32,6 +32,13 @@ struct jffs2_inodirty;
 struct jffs2_mount_opts {
 	bool override_compr;
 	unsigned int compr;
+
+	/* The size of the reserved pool. The reserved pool is the JFFS2 flash
+	 * space which may only be used by root cannot be used by the other
+	 * users. This is implemented simply by means of not allowing the
+	 * latter users to write to the file system if the amount if the
+	 * available space is less then 'rp_size'. */
+	unsigned int rp_size;
 };
 
 /* A struct for the overall file system control.  Pointers to
diff --git a/fs/jffs2/nodemgmt.c b/fs/jffs2/nodemgmt.c
index 6784d1e..0c96eb5 100644
--- a/fs/jffs2/nodemgmt.c
+++ b/fs/jffs2/nodemgmt.c
@@ -18,6 +18,37 @@
 #include "nodelist.h"
 #include "debug.h"
 
+/*
+ * Check whether the user is allowed to write.
+ */
+static int jffs2_rp_can_write(struct jffs2_sb_info *c)
+{
+	uint32_t avail;
+	struct jffs2_mount_opts *opts = &c->mount_opts;
+
+	avail = c->dirty_size + c->free_size + c->unchecked_size +
+		c->erasing_size - c->resv_blocks_write * c->sector_size
+		- c->nospc_dirty_size;
+
+	if (avail < 2 * opts->rp_size)
+		jffs2_dbg(1, "rpsize %u, dirty_size %u, free_size %u, "
+			  "erasing_size %u, unchecked_size %u, "
+			  "nr_erasing_blocks %u, avail %u, resrv %u\n",
+			  opts->rp_size, c->dirty_size, c->free_size,
+			  c->erasing_size, c->unchecked_size,
+			  c->nr_erasing_blocks, avail, c->nospc_dirty_size);
+
+	if (avail > opts->rp_size)
+		return 1;
+
+	/* Always allow root */
+	if (capable(CAP_SYS_RESOURCE))
+		return 1;
+
+	jffs2_dbg(1, "forbid writing\n");
+	return 0;
+}
+
 /**
  *	jffs2_reserve_space - request physical space to write nodes to flash
  *	@c: superblock info
@@ -55,6 +86,15 @@ int jffs2_reserve_space(struct jffs2_sb_info *c, uint32_t minsize,
 
 	spin_lock(&c->erase_completion_lock);
 
+	/*
+	 * Check if the free space is greater then size of the reserved pool.
+	 * If not, only allow root to proceed with writing.
+	 */
+	if (prio != ALLOC_DELETION && !jffs2_rp_can_write(c)) {
+		ret = -ENOSPC;
+		goto out;
+	}
+
 	/* this needs a little more thought (true <tglx> :)) */
 	while(ret == -EAGAIN) {
 		while(c->nr_free_blocks + c->nr_erasing_blocks < blocksneeded) {
@@ -158,6 +198,8 @@ int jffs2_reserve_space(struct jffs2_sb_info *c, uint32_t minsize,
 			jffs2_dbg(1, "%s(): ret is %d\n", __func__, ret);
 		}
 	}
+
+out:
 	spin_unlock(&c->erase_completion_lock);
 	if (!ret)
 		ret = jffs2_prealloc_raw_node_refs(c, c->nextblock, 1);
diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
index f9916f3..66d4456 100644
--- a/fs/jffs2/super.c
+++ b/fs/jffs2/super.c
@@ -105,6 +105,8 @@ static int jffs2_show_options(struct seq_file *s, struct dentry *root)
 
 	if (opts->override_compr)
 		seq_printf(s, ",compr=%s", jffs2_compr_name(opts->compr));
+	if (opts->rp_size)
+		seq_printf(s, ",rp_size=%u", opts->rp_size / 1024);
 
 	return 0;
 }
@@ -171,15 +173,18 @@ static const struct export_operations jffs2_export_ops = {
  * JFFS2 mount options.
  *
  * Opt_override_compr: override default compressor
+ * Opt_rp_size: size of reserved pool in KiB
  * Opt_err: just end of array marker
  */
 enum {
 	Opt_override_compr,
+	Opt_rp_size,
 	Opt_err,
 };
 
 static const match_table_t tokens = {
 	{Opt_override_compr, "compr=%s"},
+	{Opt_rp_size, "rp_size=%u"},
 	{Opt_err, NULL},
 };
 
@@ -187,6 +192,7 @@ static int jffs2_parse_options(struct jffs2_sb_info *c, char *data)
 {
 	substring_t args[MAX_OPT_ARGS];
 	char *p, *name;
+	unsigned int opt;
 
 	if (!data)
 		return 0;
@@ -224,6 +230,17 @@ static int jffs2_parse_options(struct jffs2_sb_info *c, char *data)
 			kfree(name);
 			c->mount_opts.override_compr = true;
 			break;
+		case Opt_rp_size:
+			if (match_int(&args[0], &opt))
+				return -EINVAL;
+			opt *= 1024;
+			if (opt > c->mtd->size) {
+				pr_warn("Too large reserve pool specified, max "
+					"is %llu KB\n", c->mtd->size / 1024);
+				return -EINVAL;
+			}
+			c->mount_opts.rp_size = opt;
+			break;
 		default:
 			pr_err("Error: unrecognized mount option '%s' or missing value\n",
 			       p);