[PATCH v2 3/4] vfs: allow fsinfo to fetch the current state of s_wb_err

[Jeff Layton]

From: Jeff Layton <jlay...@redhat.com>

Add a new "error_state" struct to fsinfo, and teach the kernel to fill
that out from sb->s_wb_info. There are two fields:

wb_error_last: the most recently recorded errno for the filesystem

wb_error_cookie: this value will change vs. the previously fetched
                 value if a new error was recorded since it was last
                 checked

Signed-off-by: Jeff Layton <jlay...@redhat.com>
---
 fs/statfs.c                 |  9 +++++++++
 include/uapi/linux/fsinfo.h | 11 +++++++++++
 2 files changed, 20 insertions(+)

diff --git a/fs/statfs.c b/fs/statfs.c
index fa6be965dce1..fb1f48eb381a 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -576,6 +576,14 @@ static int fsinfo_generic_io_size(struct dentry *dentry,
        return sizeof(*c);
 }
 
+static int fsinfo_generic_error_state(struct dentry *dentry,
+                                 struct fsinfo_error_state *c)
+{
+       c->wb_error_cookie = errseq_scrape(&dentry->d_sb->s_wb_err);
+       c->wb_error_last = c->wb_error_cookie & MAX_ERRNO;
+       return sizeof(*c);
+}
+
 /*
  * Implement some queries generically from stuff in the superblock.
  */
@@ -594,6 +602,7 @@ int generic_fsinfo(struct dentry *dentry, struct 
fsinfo_kparams *params)
        case _gen(volume_id);
        case _gen(name_encoding);
        case _gen(io_size);
+       case _gen(error_state);
        default:
                return -EOPNOTSUPP;
        }
diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
index f2bc5130544d..fbc5d840ea4e 100644
--- a/include/uapi/linux/fsinfo.h
+++ b/include/uapi/linux/fsinfo.h
@@ -35,6 +35,7 @@ enum fsinfo_attribute {
        fsinfo_attr_name_encoding       = 17,   /* Filename encoding (string) */
        fsinfo_attr_name_codepage       = 18,   /* Filename codepage (string) */
        fsinfo_attr_io_size             = 19,   /* Optimal I/O sizes */
+       fsinfo_attr_error_state         = 20,   /* Error state */
        fsinfo_attr__nr
 };
 
@@ -211,6 +212,16 @@ struct fsinfo_server_address {
        struct __kernel_sockaddr_storage address;
 };
 
+/*
+ * Information struct for fsinfo(fsinfo_attr_error_state).
+ *
+ * Retrieve the error state for a filesystem.
+ */
+struct fsinfo_error_state {
+       __u32           wb_error_cookie;        /* writeback error cookie */
+       __u32           wb_error_last;          /* latest writeback error */
+};
+
 /*
  * Information struct for fsinfo(fsinfo_attr_io_size).
  *
-- 
2.17.1