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Date:   Wed, 2 Jun 2021 12:02:56 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 2/2 v4] f2fs: support RO feature
Message-ID: <YLfV4EPW5Yw6wP+v@google.com>
References: <20210521190217.2484099-1-jaegeuk@kernel.org>
 <20210521190217.2484099-2-jaegeuk@kernel.org>
 <YK5UOfzwdZni7c5W@google.com>
 <YK5edM0igwfd47LV@google.com>
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Precedence: bulk

Given RO feature in superblock, we don't need to check provisioning/reserve
spaces and SSA area.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---

Change log from v3:
 - add feature sysfs entries

 fs/f2fs/f2fs.h    |  3 +++
 fs/f2fs/segment.c |  4 ++++
 fs/f2fs/super.c   | 37 +++++++++++++++++++++++++++++++------
 fs/f2fs/sysfs.c   |  8 ++++++++
 4 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index eaf57b5f3c4b..8903c43091f8 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -168,6 +168,7 @@ struct f2fs_mount_info {
 #define F2FS_FEATURE_SB_CHKSUM		0x0800
 #define F2FS_FEATURE_CASEFOLD		0x1000
 #define F2FS_FEATURE_COMPRESSION	0x2000
+#define F2FS_FEATURE_RO			0x4000
 
 #define __F2FS_HAS_FEATURE(raw_super, mask)				\
 	((raw_super->feature & cpu_to_le32(mask)) != 0)
@@ -940,6 +941,7 @@ static inline void set_new_dnode(struct dnode_of_data *dn, struct inode *inode,
 #define	NR_CURSEG_DATA_TYPE	(3)
 #define NR_CURSEG_NODE_TYPE	(3)
 #define NR_CURSEG_INMEM_TYPE	(2)
+#define NR_CURSEG_RO_TYPE	(2)
 #define NR_CURSEG_PERSIST_TYPE	(NR_CURSEG_DATA_TYPE + NR_CURSEG_NODE_TYPE)
 #define NR_CURSEG_TYPE		(NR_CURSEG_INMEM_TYPE + NR_CURSEG_PERSIST_TYPE)
 
@@ -4128,6 +4130,7 @@ F2FS_FEATURE_FUNCS(verity, VERITY);
 F2FS_FEATURE_FUNCS(sb_chksum, SB_CHKSUM);
 F2FS_FEATURE_FUNCS(casefold, CASEFOLD);
 F2FS_FEATURE_FUNCS(compression, COMPRESSION);
+F2FS_FEATURE_FUNCS(readonly, RO);
 
 #ifdef CONFIG_BLK_DEV_ZONED
 static inline bool f2fs_blkz_is_seq(struct f2fs_sb_info *sbi, int devi,
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 380ef34e1a59..376c33ab71e2 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -4683,6 +4683,10 @@ static int sanity_check_curseg(struct f2fs_sb_info *sbi)
 		struct seg_entry *se = get_seg_entry(sbi, curseg->segno);
 		unsigned int blkofs = curseg->next_blkoff;
 
+		if (F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO) &&
+			i != CURSEG_HOT_DATA && i != CURSEG_HOT_NODE)
+			continue;
+
 		sanity_check_seg_type(sbi, curseg->seg_type);
 
 		if (f2fs_test_bit(blkofs, se->cur_valid_map))
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 2fa59c674cd9..fb490383c767 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -555,7 +555,7 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
 	int ret;
 
 	if (!options)
-		return 0;
+		goto default_check;
 
 	while ((p = strsep(&options, ",")) != NULL) {
 		int token;
@@ -1090,6 +1090,7 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
 			return -EINVAL;
 		}
 	}
+default_check:
 #ifdef CONFIG_QUOTA
 	if (f2fs_check_quota_options(sbi))
 		return -EINVAL;
@@ -1162,6 +1163,11 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
 	 */
 	if (F2FS_OPTION(sbi).active_logs != NR_CURSEG_TYPE)
 		F2FS_OPTION(sbi).whint_mode = WHINT_MODE_OFF;
+
+	if (F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO) && !f2fs_readonly(sbi->sb)) {
+		f2fs_err(sbi, "Allow to mount readonly mode only");
+		return -EROFS;
+	}
 	return 0;
 }
 
@@ -1819,7 +1825,11 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 static void default_options(struct f2fs_sb_info *sbi)
 {
 	/* init some FS parameters */
-	F2FS_OPTION(sbi).active_logs = NR_CURSEG_PERSIST_TYPE;
+	if (F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO))
+		F2FS_OPTION(sbi).active_logs = NR_CURSEG_RO_TYPE;
+	else
+		F2FS_OPTION(sbi).active_logs = NR_CURSEG_PERSIST_TYPE;
+
 	F2FS_OPTION(sbi).inline_xattr_size = DEFAULT_INLINE_XATTR_ADDRS;
 	F2FS_OPTION(sbi).whint_mode = WHINT_MODE_OFF;
 	F2FS_OPTION(sbi).alloc_mode = ALLOC_MODE_DEFAULT;
@@ -2001,6 +2011,11 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 	if (f2fs_readonly(sb) && (*flags & SB_RDONLY))
 		goto skip;
 
+	if (F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO) && !(*flags & SB_RDONLY)) {
+		err = -EROFS;
+		goto restore_opts;
+	}
+
 #ifdef CONFIG_QUOTA
 	if (!f2fs_readonly(sb) && (*flags & SB_RDONLY)) {
 		err = dquot_suspend(sb, -1);
@@ -3134,14 +3149,15 @@ int f2fs_sanity_check_ckpt(struct f2fs_sb_info *sbi)
 	ovp_segments = le32_to_cpu(ckpt->overprov_segment_count);
 	reserved_segments = le32_to_cpu(ckpt->rsvd_segment_count);
 
-	if (unlikely(fsmeta < F2FS_MIN_META_SEGMENTS ||
+	if (!F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO) &&
+			unlikely(fsmeta < F2FS_MIN_META_SEGMENTS ||
 			ovp_segments == 0 || reserved_segments == 0)) {
 		f2fs_err(sbi, "Wrong layout: check mkfs.f2fs version");
 		return 1;
 	}
-
 	user_block_count = le64_to_cpu(ckpt->user_block_count);
-	segment_count_main = le32_to_cpu(raw_super->segment_count_main);
+	segment_count_main = le32_to_cpu(raw_super->segment_count_main) +
+			(F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO) ? 1 : 0);
 	log_blocks_per_seg = le32_to_cpu(raw_super->log_blocks_per_seg);
 	if (!user_block_count || user_block_count >=
 			segment_count_main << log_blocks_per_seg) {
@@ -3172,6 +3188,10 @@ int f2fs_sanity_check_ckpt(struct f2fs_sb_info *sbi)
 		if (le32_to_cpu(ckpt->cur_node_segno[i]) >= main_segs ||
 			le16_to_cpu(ckpt->cur_node_blkoff[i]) >= blocks_per_seg)
 			return 1;
+
+		if (F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO))
+			goto check_data;
+
 		for (j = i + 1; j < NR_CURSEG_NODE_TYPE; j++) {
 			if (le32_to_cpu(ckpt->cur_node_segno[i]) ==
 				le32_to_cpu(ckpt->cur_node_segno[j])) {
@@ -3182,10 +3202,15 @@ int f2fs_sanity_check_ckpt(struct f2fs_sb_info *sbi)
 			}
 		}
 	}
+check_data:
 	for (i = 0; i < NR_CURSEG_DATA_TYPE; i++) {
 		if (le32_to_cpu(ckpt->cur_data_segno[i]) >= main_segs ||
 			le16_to_cpu(ckpt->cur_data_blkoff[i]) >= blocks_per_seg)
 			return 1;
+
+		if (F2FS_HAS_FEATURE(sbi, F2FS_FEATURE_RO))
+			goto skip_cross;
+
 		for (j = i + 1; j < NR_CURSEG_DATA_TYPE; j++) {
 			if (le32_to_cpu(ckpt->cur_data_segno[i]) ==
 				le32_to_cpu(ckpt->cur_data_segno[j])) {
@@ -3207,7 +3232,7 @@ int f2fs_sanity_check_ckpt(struct f2fs_sb_info *sbi)
 			}
 		}
 	}
-
+skip_cross:
 	sit_bitmap_size = le32_to_cpu(ckpt->sit_ver_bitmap_bytesize);
 	nat_bitmap_size = le32_to_cpu(ckpt->nat_ver_bitmap_bytesize);
 
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 09e3f258eb52..62fbe4f20dd6 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -158,6 +158,9 @@ static ssize_t features_show(struct f2fs_attr *a,
 	if (f2fs_sb_has_casefold(sbi))
 		len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
 				len ? ", " : "", "casefold");
+	if (f2fs_sb_has_readonly(sbi))
+		len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
+				len ? ", " : "", "readonly");
 	if (f2fs_sb_has_compression(sbi))
 		len += scnprintf(buf + len, PAGE_SIZE - len, "%s%s",
 				len ? ", " : "", "compression");
@@ -578,6 +581,7 @@ enum feat_id {
 	FEAT_SB_CHECKSUM,
 	FEAT_CASEFOLD,
 	FEAT_COMPRESSION,
+	FEAT_RO,
 	FEAT_TEST_DUMMY_ENCRYPTION_V2,
 };
 
@@ -599,6 +603,7 @@ static ssize_t f2fs_feature_show(struct f2fs_attr *a,
 	case FEAT_SB_CHECKSUM:
 	case FEAT_CASEFOLD:
 	case FEAT_COMPRESSION:
+	case FEAT_RO:
 	case FEAT_TEST_DUMMY_ENCRYPTION_V2:
 		return sprintf(buf, "supported\n");
 	}
@@ -723,12 +728,14 @@ F2FS_FEATURE_RO_ATTR(sb_checksum, FEAT_SB_CHECKSUM);
 #ifdef CONFIG_UNICODE
 F2FS_FEATURE_RO_ATTR(casefold, FEAT_CASEFOLD);
 #endif
+F2FS_FEATURE_RO_ATTR(readonly, FEAT_RO);
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 F2FS_FEATURE_RO_ATTR(compression, FEAT_COMPRESSION);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, compr_written_block, compr_written_block);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, compr_saved_block, compr_saved_block);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, compr_new_inode, compr_new_inode);
 #endif
+
 /* For ATGC */
 F2FS_RW_ATTR(ATGC_INFO, atgc_management, atgc_candidate_ratio, candidate_ratio);
 F2FS_RW_ATTR(ATGC_INFO, atgc_management, atgc_candidate_count, max_candidate_count);
@@ -834,6 +841,7 @@ static struct attribute *f2fs_feat_attrs[] = {
 #ifdef CONFIG_UNICODE
 	ATTR_LIST(casefold),
 #endif
+	ATTR_LIST(readonly),
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 	ATTR_LIST(compression),
 #endif
-- 
2.32.0.rc0.204.g9fa02ecfa5-goog