erofs: adjust per-CPU buffers according to max_pclusterblks

Adjust per-CPU buffers on demand since big pcluster definition is
available. Also, bail out unsupported pcluster size according to
Z_EROFS_PCLUSTER_MAX_SIZE.

Link: https://lore.kernel.org/r/20210407043927.10623-7-xiang@kernel.org
Acked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

fs/erofs/decompressor.c

@@ -32,6 +32,7 @@ int z_erofs_load_lz4_config(struct super_block *sb,
 			    struct erofs_super_block *dsb,
 			    struct z_erofs_lz4_cfgs *lz4, int size)
 {
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
 	u16 distance;
 
 	if (lz4) {
@@ -40,16 +41,27 @@ int z_erofs_load_lz4_config(struct super_block *sb,
 			return -EINVAL;
 		}
 		distance = le16_to_cpu(lz4->max_distance);
+
+		sbi->lz4.max_pclusterblks = le16_to_cpu(lz4->max_pclusterblks);
+		if (!sbi->lz4.max_pclusterblks) {
+			sbi->lz4.max_pclusterblks = 1;	/* reserved case */
+		} else if (sbi->lz4.max_pclusterblks >
+			   Z_EROFS_PCLUSTER_MAX_SIZE / EROFS_BLKSIZ) {
+			erofs_err(sb, "too large lz4 pclusterblks %u",
+				  sbi->lz4.max_pclusterblks);
+			return -EINVAL;
+		} else if (sbi->lz4.max_pclusterblks >= 2) {
+			erofs_info(sb, "EXPERIMENTAL big pcluster feature in use. Use at your own risk!");
+		}
 	} else {
 		distance = le16_to_cpu(dsb->u1.lz4_max_distance);
+		sbi->lz4.max_pclusterblks = 1;
 	}
 
-	EROFS_SB(sb)->lz4.max_distance_pages = distance ?
+	sbi->lz4.max_distance_pages = distance ?
 					DIV_ROUND_UP(distance, PAGE_SIZE) + 1 :
 					LZ4_MAX_DISTANCE_PAGES;
-
-	/* TODO: use max pclusterblks after bigpcluster is enabled */
-	return erofs_pcpubuf_growsize(1);
+	return erofs_pcpubuf_growsize(sbi->lz4.max_pclusterblks);
 }
 
 static int z_erofs_lz4_prepare_destpages(struct z_erofs_decompress_req *rq,

fs/erofs/internal.h

@@ -63,6 +63,8 @@ struct erofs_fs_context {
 struct erofs_sb_lz4_info {
 	/* # of pages needed for EROFS lz4 rolling decompression */
 	u16 max_distance_pages;
+	/* maximum possible blocks for pclusters in the filesystem */
+	u16 max_pclusterblks;
 };
 
 struct erofs_sb_info {