Add fault injection with wrong storage capacity

With error injection `errinj_wrong_capacity` filesystem reports a wrong
storage capacity. Problem simulated with `errinj_wrong_capacity` may
happen in real. For instance see a case described in SQLite
documentation: "There are many fraudulent USB sticks in circulation that
report to have a high capacity (ex: 8GB) but are really only capable of
storing a much smaller amount (ex: 1GB). Attempts to write on these
devices will often result in unrelated files being overwritten. Any use
of a fraudulent flash memory device can easily lead to database
corruption, therefore."

1. https://www.sqlite.org/howtocorrupt.html

Closes #62

wrong

README.md

@@ -15,6 +15,9 @@ Supported fault injections are:
 - `errinj_slowdown` - slowdown invoked file operation.
 - `errinj_1byte_read` - amount of data returned by `read()` call is always
   limited by a single byte.
+- `errinj_wrong_capacity` - filesystem reports a wrong storage capacity.
+  Simulated error can happen in a wild, for instance see '4.2. Fake capacity USB
+  sticks' in [How To Corrupt An SQLite Database File](https://www.sqlite.org/howtocorrupt.html).
 
 ### Building
 

unreliablefs.conf.5

@@ -40,6 +40,8 @@ File operation slowdown for nanoseconds specified by duration parameter.
 Return exactly 1 byte on every
 .Xr read 2
 operation.
+.It Cm errinj_wrong_capacity
+Report a wrong storage capacity.
 .El
 .Pp
 The options are:

unreliablefs_errinj.c

@@ -22,6 +22,7 @@ const char *errinj_name[] =
     "errinj_noop",
     "errinj_slowdown",
     "errinj_1byte_read",
+    "errinj_wrong_capacity",
 };
 
 typedef enum {
@@ -30,6 +31,7 @@ typedef enum {
     ERRINJ_NOOP,
     ERRINJ_SLOWDOWN,
     ERRINJ_1BYTE_READ,
+    ERRINJ_WRONG_CAPACITY,
 } errinj_type;
 
 typedef struct errinj_conf errinj_conf;
@@ -269,6 +271,10 @@ int error_inject(const char* path, fuse_op operation)
             if (strcmp(op_name, "read") == 0)
                 rc = -ERRINJ_1BYTE_READ;
             break;
+        case ERRINJ_WRONG_CAPACITY:
+            if (strcmp(op_name, "statfs") == 0)
+                rc = -ERRNO_WRONG_CAPACITY;
+            break;
         }
     }
 

unreliablefs_errinj.h

@@ -23,6 +23,7 @@
 #define MAX_PROBABLITY 100
 #define ERRNO_NOOP -999
 #define ERRNO_1BYTE_READ -998
+#define ERRNO_WRONG_CAPACITY -997
 #define DEFAULT_SIGNAL_NAME SIGKILL
 
 int error_inject(const char* path, fuse_op operation);

unreliablefs_ops.c

@@ -386,6 +386,14 @@ int unreliable_statfs(const char *path, struct statvfs *buf)
     int ret = error_inject(path, OP_STATFS);
     if (ret == -ERRNO_NOOP) {
         return 0;
+    } else if (ret == -ERRNO_WRONG_CAPACITY) {
+        /* wrong capacity */
+        ret = statvfs(path, buf);
+        if (ret == -1) {
+            return -errno;
+        }
+	buf->f_bfree = buf->f_bfree + ( 5 / 100.0 ) * (uint64_t)buf->f_bfree;
+	return 0;
     } else if (ret) {
         return ret;
     }