Let's add .get_acl() to read the file's acl from its xattrs
to make POSIX ACL usable.

Here is the on-disk detail,
fullname: system.posix_acl_access
struct erofs_xattr_entry:
        .e_name_len = 0
        .e_name_index = EROFS_XATTR_INDEX_POSIX_ACL_ACCESS (2)

fullname: system.posix_acl_default
struct erofs_xattr_entry:
        .e_name_len = 0
        .e_name_index = EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT (3)

Signed-off-by: Gao Xiang <gaoxian...@huawei.com>
---
change log v2:
 - add the missing SB_POSIXACL flag;
 - fix the on-disk detail, use .e_name_len == 0 and proper prefix value;
 - tested ok with xattr enabled erofs_mkfs;

 .../erofs/Documentation/filesystems/erofs.txt      |  2 ++
 drivers/staging/erofs/inode.c                      |  3 ++
 drivers/staging/erofs/namei.c                      |  1 +
 drivers/staging/erofs/super.c                      |  8 +++++
 drivers/staging/erofs/xattr.c                      | 37 ++++++++++++++++++++++
 drivers/staging/erofs/xattr.h                      |  6 ++++
 6 files changed, 57 insertions(+)

diff --git a/drivers/staging/erofs/Documentation/filesystems/erofs.txt 
b/drivers/staging/erofs/Documentation/filesystems/erofs.txt
index 803988d74c21..961ec4da7705 100644
--- a/drivers/staging/erofs/Documentation/filesystems/erofs.txt
+++ b/drivers/staging/erofs/Documentation/filesystems/erofs.txt
@@ -36,6 +36,8 @@ Here is the main features of EROFS:
 
  - Support xattr inline and tail-end data inline for all files;
 
+ - Support POSIX.1e ACLs by using xattrs;
+
  - Support transparent file compression as an option:
    LZ4 algorithm with 4 KB fixed-output compression for high performance;
 
diff --git a/drivers/staging/erofs/inode.c b/drivers/staging/erofs/inode.c
index 4f04f7c38cf2..924b8dfc7a8f 100644
--- a/drivers/staging/erofs/inode.c
+++ b/drivers/staging/erofs/inode.c
@@ -287,6 +287,7 @@ const struct inode_operations erofs_generic_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
        .listxattr = erofs_listxattr,
 #endif
+       .get_acl = erofs_get_acl,
 };
 
 const struct inode_operations erofs_symlink_iops = {
@@ -294,6 +295,7 @@ const struct inode_operations erofs_symlink_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
        .listxattr = erofs_listxattr,
 #endif
+       .get_acl = erofs_get_acl,
 };
 
 const struct inode_operations erofs_fast_symlink_iops = {
@@ -301,5 +303,6 @@ const struct inode_operations erofs_fast_symlink_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
        .listxattr = erofs_listxattr,
 #endif
+       .get_acl = erofs_get_acl,
 };
 
diff --git a/drivers/staging/erofs/namei.c b/drivers/staging/erofs/namei.c
index 7fed1f996ab0..b1752adc5934 100644
--- a/drivers/staging/erofs/namei.c
+++ b/drivers/staging/erofs/namei.c
@@ -238,5 +238,6 @@ const struct inode_operations erofs_dir_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
        .listxattr = erofs_listxattr,
 #endif
+       .get_acl = erofs_get_acl,
 };
 
diff --git a/drivers/staging/erofs/super.c b/drivers/staging/erofs/super.c
index 176fca2af379..54cd7dac0a1f 100644
--- a/drivers/staging/erofs/super.c
+++ b/drivers/staging/erofs/super.c
@@ -398,6 +398,14 @@ static int erofs_read_super(struct super_block *sb,
        if (!silent)
                infoln("root inode @ nid %llu", ROOT_NID(sbi));
 
+#ifdef CONFIG_EROFS_FS_POSIX_ACL
+       /* Update the POSIXACL Flag */
+       if (test_opt(sbi, POSIX_ACL))
+               sb->s_flags |= SB_POSIXACL;
+       else
+               sb->s_flags &= ~SB_POSIXACL;
+#endif
+
 #ifdef CONFIG_EROFS_FS_ZIP
        INIT_RADIX_TREE(&sbi->workstn_tree, GFP_ATOMIC);
 #endif
diff --git a/drivers/staging/erofs/xattr.c b/drivers/staging/erofs/xattr.c
index 7de46690d972..6759485ae862 100644
--- a/drivers/staging/erofs/xattr.c
+++ b/drivers/staging/erofs/xattr.c
@@ -643,3 +643,40 @@ ssize_t erofs_listxattr(struct dentry *dentry,
        return shared_listxattr(&it);
 }
 
+#ifdef CONFIG_EROFS_FS_POSIX_ACL
+struct posix_acl *erofs_get_acl(struct inode *inode, int type)
+{
+       struct posix_acl *acl;
+       int ea_prefix, rc;
+       char *value = NULL;
+
+       switch(type) {
+       case ACL_TYPE_ACCESS:
+               ea_prefix = EROFS_XATTR_INDEX_POSIX_ACL_ACCESS;
+               break;
+       case ACL_TYPE_DEFAULT:
+               ea_prefix = EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT;
+               break;
+       default:
+               return ERR_PTR(-EINVAL);
+       }
+
+       rc = erofs_getxattr(inode, ea_prefix, "", NULL, 0);
+       if (rc > 0) {
+               value = kvmalloc(rc, GFP_KERNEL);
+               if (!value)
+                       return ERR_PTR(-ENOMEM);
+               rc = erofs_getxattr(inode, ea_prefix, "", value, rc);
+       }
+
+       if (rc == -ENOATTR)
+               acl = NULL;
+       else if (rc < 0)
+               acl = ERR_PTR(rc);
+       else
+               acl = posix_acl_from_xattr(&init_user_ns, value, rc);
+       kvfree(value);
+       return acl;
+}
+#endif
+
diff --git a/drivers/staging/erofs/xattr.h b/drivers/staging/erofs/xattr.h
index 634dae9aaa0b..35ba5ac2139a 100644
--- a/drivers/staging/erofs/xattr.h
+++ b/drivers/staging/erofs/xattr.h
@@ -87,5 +87,11 @@ static ssize_t __maybe_unused erofs_listxattr(struct dentry 
*dentry,
 }
 #endif
 
+#ifdef CONFIG_EROFS_FS_POSIX_ACL
+struct posix_acl *erofs_get_acl(struct inode *inode, int type);
+#else
+#define erofs_get_acl  (NULL)
+#endif
+
 #endif
 
-- 
2.14.4

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