When mounting a UFS filesystem, return EINTEGRITY rather than EIO

when a superblock check-hash error is detected. This change clarifies
a mount that failed due to media hardware failures (EIO) from a mount
that failed due to media errors (EINTEGRITY) that can be corrected by
running fsck(8).

Sponsored by: Netflix

lib/libc/sys/mount.2

@@ -307,6 +307,10 @@ No space remains in the mount table.
 .It Bq Er EINVAL
 The super block for the file system had a bad magic
 number or an out of range block size.
+.It Bq Er EINTEGRITY
+The super block for the file system had a bad check hash.
+The check hash can usually be corrected by running
+.Xr fsck 8 .
 .It Bq Er ENOMEM
 Not enough memory was available to read the cylinder
 group information for the file system.

sys/ufs/ffs/ffs_subr.c

@@ -416,7 +416,7 @@ readsuper(void *devfd, struct fs **fsp, off_t sblockloc, int isaltsblk,
 				return (0);
 			}
 			fs->fs_fmod = 0;
-			return (EINVAL);
+			return (EINTEGRITY);
 		}
 		/* Have to set for old filesystems that predate this field */
 		fs->fs_sblockactualloc = sblockloc;