ext4: add new attr pointer attr_mb_order

The s_mb_best_avail_max_trim_order is of type unsigned int, and has a
range of values well beyond the normal use of the mb_order. Although the
mballoc code is careful enough that large numbers don't matter there, but
this can mislead the sysadmin into thinking that it's normal to set such
values. Hence add a new attr_id attr_mb_order with values in the range
[0, 64] to avoid storing garbage values and make us more resilient to
surprises in the future.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240319113325.3110393-6-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index ddd71673176c34f662d790f5f6d8fbe926258b1f..8e04731694587aefaee851e4402d4dd50f823d7f 100644 (file)
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -30,6 +30,7 @@ typedef enum {
        attr_first_error_time,
        attr_last_error_time,
        attr_clusters_in_group,
+       attr_mb_order,
        attr_feature,
        attr_pointer_ui,
        attr_pointer_ul,
@@ -210,6 +211,8 @@ EXT4_ATTR_OFFSET(inode_readahead_blks, 0644, inode_readahead,
                 ext4_sb_info, s_inode_readahead_blks);
 EXT4_ATTR_OFFSET(mb_group_prealloc, 0644, clusters_in_group,
                 ext4_sb_info, s_mb_group_prealloc);
+EXT4_ATTR_OFFSET(mb_best_avail_max_trim_order, 0644, mb_order,
+                ext4_sb_info, s_mb_best_avail_max_trim_order);
 EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal);
 EXT4_RW_ATTR_SBI_UI(mb_stats, s_mb_stats);
 EXT4_RW_ATTR_SBI_UI(mb_max_to_scan, s_mb_max_to_scan);
@@ -225,7 +228,6 @@ EXT4_RW_ATTR_SBI_UI(warning_ratelimit_interval_ms, s_warning_ratelimit_state.int
 EXT4_RW_ATTR_SBI_UI(warning_ratelimit_burst, s_warning_ratelimit_state.burst);
 EXT4_RW_ATTR_SBI_UI(msg_ratelimit_interval_ms, s_msg_ratelimit_state.interval);
 EXT4_RW_ATTR_SBI_UI(msg_ratelimit_burst, s_msg_ratelimit_state.burst);
-EXT4_RW_ATTR_SBI_UI(mb_best_avail_max_trim_order, s_mb_best_avail_max_trim_order);
 #ifdef CONFIG_EXT4_DEBUG
 EXT4_RW_ATTR_SBI_UL(simulate_fail, s_simulate_fail);
 #endif
@@ -379,6 +381,7 @@ static ssize_t ext4_generic_attr_show(struct ext4_attr *a,
        switch (a->attr_id) {
        case attr_inode_readahead:
        case attr_clusters_in_group:
+       case attr_mb_order:
        case attr_pointer_ui:
                if (a->attr_ptr == ptr_ext4_super_block_offset)
                        return sysfs_emit(buf, "%u\n", le32_to_cpup(ptr));
@@ -458,6 +461,14 @@ static ssize_t ext4_generic_attr_store(struct ext4_attr *a,
                else
                        *((unsigned int *) ptr) = t;
                return len;
+       case attr_mb_order:
+               ret = kstrtouint(skip_spaces(buf), 0, &t);
+               if (ret)
+                       return ret;
+               if (t > 64)
+                       return -EINVAL;
+               *((unsigned int *) ptr) = t;
+               return len;
        case attr_clusters_in_group:
                ret = kstrtouint(skip_spaces(buf), 0, &t);
                if (ret)