[RFC PATCH v1 3/6] btrfs: Create btrfs CPU set struct and helpers

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

It's a preparation to add Btrfs CPU affinity support. First, create a
new struct named `btrfs_cpu_set` to contain CPU affinity information.
Then, create helpers to allocate, parse, and free them.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 fs/btrfs/fs.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/fs.h |  7 ++++
 2 files changed, 104 insertions(+)

diff --git a/fs/btrfs/fs.c b/fs/btrfs/fs.c
index 31c1648bc0b46922..283d153d4491289c 100644
--- a/fs/btrfs/fs.c
+++ b/fs/btrfs/fs.c
@@ -96,3 +96,100 @@ void __btrfs_clear_fs_compat_ro(struct btrfs_fs_info *fs_info, u64 flag,
 		set_bit(BTRFS_FS_FEATURE_CHANGED, &fs_info->flags);
 	}
 }
+
+/*
+ * The user can't use the taskset pattern because ',' is used as
+ * the mount option delimiter. They can use the same taskset pattern,
+ * but replace the ',' with '.' and we will replace it back to
+ * ',', so the cpulist_parse() can recognize it.
+ *
+ * For example, in taskset cmd, they do:
+ * taskset -c 1,4,7 /bin/ls
+ *
+ * The equivalent CPU mask for the btrfs mount option will be:
+ * wq_cpu_set=1.4.7
+ *
+ * Mark these as __cold to avoid the code bloat from overoptimizing
+ * the loop.
+ */
+__cold static void cpulist_dot_to_comma(char *set)
+{
+	while (*set) {
+		if (*set == '.')
+			*set = ',';
+		set++;
+	}
+}
+
+__cold static void cpulist_comma_to_dot(char *set)
+{
+	while (*set) {
+		if (*set == ',')
+			*set = '.';
+		set++;
+	}
+}
+
+void btrfs_destroy_cpu_set(struct btrfs_cpu_set *cpu_set)
+{
+	if (!cpu_set)
+		return;
+
+	free_cpumask_var(cpu_set->mask);
+	kfree(cpu_set->mask_str);
+	kfree(cpu_set);
+}
+
+/*
+ * Only called from btrfs_parse_cpu_set().
+ */
+static struct btrfs_cpu_set *btrfs_alloc_cpu_set(void)
+{
+	struct btrfs_cpu_set *cpu_set;
+
+	cpu_set = kmalloc(sizeof(*cpu_set), GFP_KERNEL);
+	if (!cpu_set)
+		return NULL;
+
+	if (!alloc_cpumask_var(&cpu_set->mask, GFP_KERNEL)) {
+		kfree(cpu_set);
+		return NULL;
+	}
+
+	cpu_set->mask_str = NULL;
+	return cpu_set;
+}
+
+int btrfs_parse_cpu_set(struct btrfs_cpu_set **cpu_set_p, const char *mask_str)
+{
+	struct btrfs_cpu_set *cpu_set;
+	int ret;
+
+	cpu_set = btrfs_alloc_cpu_set();
+	if (!cpu_set)
+		return -ENOMEM;
+
+	cpu_set->mask_str = kstrdup(mask_str, GFP_KERNEL);
+	if (!cpu_set->mask_str) {
+		ret = -ENOMEM;
+		goto out_fail;
+	}
+
+	cpulist_dot_to_comma(cpu_set->mask_str);
+	ret = cpulist_parse(cpu_set->mask_str, cpu_set->mask);
+	if (ret)
+		goto out_fail;
+
+	if (cpumask_empty(cpu_set->mask)) {
+		ret = -EINVAL;
+		goto out_fail;
+	}
+
+	cpulist_comma_to_dot(cpu_set->mask_str);
+	*cpu_set_p = cpu_set;
+	return 0;
+
+out_fail:
+	btrfs_destroy_cpu_set(cpu_set);
+	return ret;
+}
diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
index 6de61367b6686197..cbad856df197ccfd 100644
--- a/fs/btrfs/fs.h
+++ b/fs/btrfs/fs.h
@@ -356,6 +356,11 @@ struct btrfs_commit_stats {
 	u64 total_commit_dur;
 };
 
+struct btrfs_cpu_set {
+	cpumask_var_t mask;
+	char *mask_str;
+};
+
 struct btrfs_fs_info {
 	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
 	unsigned long flags;
@@ -876,6 +881,8 @@ void btrfs_exclop_start_unlock(struct btrfs_fs_info *fs_info);
 void btrfs_exclop_finish(struct btrfs_fs_info *fs_info);
 void btrfs_exclop_balance(struct btrfs_fs_info *fs_info,
 			  enum btrfs_exclusive_operation op);
+int btrfs_parse_cpu_set(struct btrfs_cpu_set **cpu_set_p, const char *mask_str);
+void btrfs_destroy_cpu_set(struct btrfs_cpu_set *cpu_set);
 
 /* Compatibility and incompatibility defines */
 void __btrfs_set_fs_incompat(struct btrfs_fs_info *fs_info, u64 flag,
-- 
Ammar Faizi