[PATCHv4 01/10] reiser4: block_alloc: add BA_SOME_SPACE flag for grabbing a fixed amount of space.

[Ivan Shapovalov <intelfx100@gmail.com>]

This is used for FITRIM ioctl which will iteratively grab, allocate and trim disk space
bit by bit to avoid starving the rest of system.

Signed-off-by: Ivan Shapovalov <intelfx100@gmail.com>
---
 fs/reiser4/block_alloc.c | 22 ++++++++++++++++++----
 fs/reiser4/block_alloc.h |  5 ++++-
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/fs/reiser4/block_alloc.c b/fs/reiser4/block_alloc.c
index 324b11c..14dd378 100644
--- a/fs/reiser4/block_alloc.c
+++ b/fs/reiser4/block_alloc.c
@@ -264,7 +264,7 @@ int reiser4_check_block_counters(const struct super_block *super)
 static int
 reiser4_grab(reiser4_context * ctx, __u64 count, reiser4_ba_flags_t flags)
 {
-	__u64 free_blocks;
+	__s64 allowed_blocks;
 	int ret = 0, use_reserved = flags & BA_RESERVED;
 	reiser4_super_info_data *sbinfo;
 
@@ -280,10 +280,24 @@ reiser4_grab(reiser4_context * ctx, __u64 count, reiser4_ba_flags_t flags)
 
 	spin_lock_reiser4_super(sbinfo);
 
-	free_blocks = sbinfo->blocks_free;
+	allowed_blocks = use_reserved ? sbinfo->blocks_free
+	                              : sbinfo->blocks_free - sbinfo->blocks_reserved;
 
-	if ((use_reserved && free_blocks < count) ||
-	    (!use_reserved && free_blocks < count + sbinfo->blocks_reserved)) {
+	if (flags & BA_SOME_SPACE) {
+		/* Reserve 25% of all free space */
+		if (allowed_blocks <= 0) {
+			/* No space at all */
+			ret = RETERR(-ENOSPC);
+			goto unlock_and_ret;
+		}
+
+		count = allowed_blocks >> 2;
+		if (count == 0) {
+			/* Less than 4 free blocks */
+			count = allowed_blocks;
+		}
+	} else if (count > allowed_blocks) {
+		/* Not enough space */
 		ret = RETERR(-ENOSPC);
 		goto unlock_and_ret;
 	}
diff --git a/fs/reiser4/block_alloc.h b/fs/reiser4/block_alloc.h
index a4e98af..bfc6be9 100644
--- a/fs/reiser4/block_alloc.h
+++ b/fs/reiser4/block_alloc.h
@@ -79,7 +79,10 @@ enum reiser4_ba_flags {
 	BA_FORCE = (1 << 5),
 
 	/* use default start value for free blocks search. */
-	BA_USE_DEFAULT_SEARCH_START = (1 << 6)
+	BA_USE_DEFAULT_SEARCH_START = (1 << 6),
+
+	/* reserve some fixed amount of space */
+	BA_SOME_SPACE = (1 << 7),
 };
 
 typedef enum reiser4_ba_flags reiser4_ba_flags_t;
-- 
2.1.3