erofs: support user-defined fingerprint name

When creating the EROFS image, users can specify the fingerprint name.
This is to prepare for the upcoming inode page cache share.

Signed-off-by: Hongzhen Luo <hongzhen@linux.alibaba.com>
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Author: Hongzhen Luo

fs/erofs/Kconfig

@@ -194,3 +194,12 @@ config EROFS_FS_PCPU_KTHREAD_HIPRI
 	  at higher priority.
 
 	  If unsure, say N.
+
+config EROFS_FS_PAGE_CACHE_SHARE
+	bool "EROFS page cache share support (experimental)"
+	depends on EROFS_FS && EROFS_FS_XATTR && !EROFS_FS_ONDEMAND
+	help
+	  This enables page cache sharing among inodes with identical
+	  content fingerprints on the same machine.
+
+	  If unsure, say N.

fs/erofs/erofs_fs.h

@@ -17,7 +17,7 @@
 #define EROFS_FEATURE_COMPAT_XATTR_FILTER		0x00000004
 #define EROFS_FEATURE_COMPAT_SHARED_EA_IN_METABOX	0x00000008
 #define EROFS_FEATURE_COMPAT_PLAIN_XATTR_PFX		0x00000010
-
+#define EROFS_FEATURE_COMPAT_ISHARE_XATTRS		0x00000020
 
 /*
  * Any bits that aren't in EROFS_ALL_FEATURE_INCOMPAT should
@@ -83,7 +83,8 @@ struct erofs_super_block {
 	__le32 xattr_prefix_start;	/* start of long xattr prefixes */
 	__le64 packed_nid;	/* nid of the special packed inode */
 	__u8 xattr_filter_reserved; /* reserved for xattr name filter */
-	__u8 reserved[3];
+	__u8 ishare_xattr_prefix_id;
+	__u8 reserved[2];
 	__le32 build_time;	/* seconds added to epoch for mkfs time */
 	__le64 rootnid_8b;	/* (48BIT on) nid of root directory */
 	__le64 reserved2;

fs/erofs/internal.h

@@ -131,6 +131,7 @@ struct erofs_sb_info {
 	u32 xattr_blkaddr;
 	u32 xattr_prefix_start;
 	u8 xattr_prefix_count;
+	u8 ishare_xattr_prefix_id;
 	struct erofs_xattr_prefix_item *xattr_prefixes;
 	unsigned int xattr_filter_reserved;
 #endif
@@ -235,6 +236,7 @@ EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
 EROFS_FEATURE_FUNCS(xattr_filter, compat, COMPAT_XATTR_FILTER)
 EROFS_FEATURE_FUNCS(shared_ea_in_metabox, compat, COMPAT_SHARED_EA_IN_METABOX)
 EROFS_FEATURE_FUNCS(plain_xattr_pfx, compat, COMPAT_PLAIN_XATTR_PFX)
+EROFS_FEATURE_FUNCS(ishare_xattrs, compat, COMPAT_ISHARE_XATTRS)
 
 static inline u64 erofs_nid_to_ino64(struct erofs_sb_info *sbi, erofs_nid_t nid)
 {

fs/erofs/super.c

@@ -320,6 +320,15 @@ static int erofs_read_superblock(struct super_block *sb)
 	sbi->xattr_prefix_start = le32_to_cpu(dsb->xattr_prefix_start);
 	sbi->xattr_prefix_count = dsb->xattr_prefix_count;
 	sbi->xattr_filter_reserved = dsb->xattr_filter_reserved;
+	if (erofs_sb_has_ishare_xattrs(sbi)) {
+		if (dsb->ishare_xattr_prefix_id >= sbi->xattr_prefix_count) {
+			erofs_err(sb, "invalid ishare xattr prefix id %u",
+				  dsb->ishare_xattr_prefix_id);
+			ret = -EFSCORRUPTED;
+			goto out;
+		}
+		sbi->ishare_xattr_prefix_id = dsb->ishare_xattr_prefix_id;
+	}
 #endif
 	sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
 	if (erofs_sb_has_48bit(sbi) && dsb->rootnid_8b) {

fs/erofs/xattr.c

@@ -530,6 +530,19 @@ int erofs_xattr_prefixes_init(struct super_block *sb)
 	}
 
 	erofs_put_metabuf(&buf);
+	if (!ret && erofs_sb_has_ishare_xattrs(sbi)) {
+		struct erofs_xattr_prefix_item *pf = pfs + sbi->ishare_xattr_prefix_id;
+		struct erofs_xattr_long_prefix *newpfx;
+
+		newpfx = krealloc(pf->prefix,
+			sizeof(*newpfx) + pf->infix_len + 1, GFP_KERNEL);
+		if (newpfx) {
+			newpfx->infix[pf->infix_len] = '\0';
+			pf->prefix = newpfx;
+		} else {
+			ret = -ENOMEM;
+		}
+	}
 	sbi->xattr_prefixes = pfs;
 	if (ret)
 		erofs_xattr_prefixes_cleanup(sb);