Add fault injection with 1-byte reads

Closes #86

README.md

@@ -13,6 +13,8 @@ Supported fault injections are:
   (similar to [libeatmydata](https://github.com/stewartsmith/libeatmydata),
   but applicable to any file operation).
 - `errinj_slowdown` - slowdown invoked file operation.
+- `errinj_1byte_read` - amount of data returned by `read()` call is always
+  limited by a single byte.
 
 ### Building
 

unreliablefs.conf.5

@@ -36,6 +36,10 @@ Set random errno.
 limited by supported errno's.
 .It Cm errinj_slowdown
 File operation slowdown for nanoseconds specified by duration parameter.
+.It Cm errinj_1byte_read
+Return exactly 1 byte on every
+.Xr read 2
+operation.
 .El
 .Pp
 The options are:

unreliablefs_errinj.c

@@ -21,13 +21,15 @@ const char *errinj_name[] =
     "errinj_kill_caller",
     "errinj_noop",
     "errinj_slowdown",
+    "errinj_1byte_read",
 };
 
 typedef enum {
     ERRINJ_ERRNO,
     ERRINJ_KILL_CALLER,
     ERRINJ_NOOP,
     ERRINJ_SLOWDOWN,
+    ERRINJ_1BYTE_READ,
 } errinj_type;
 
 typedef struct errinj_conf errinj_conf;
@@ -262,6 +264,11 @@ int error_inject(const char* path, fuse_op operation)
 		fprintf(stdout, "end of '%s' slowdown with '%d' ns\n", op_name, err->duration);
             }
             break;
+        case ERRINJ_1BYTE_READ:
+            fprintf(stdout, "start of 1-byte read\n");
+            if (strcmp(op_name, "read") == 0)
+                rc = -ERRINJ_1BYTE_READ;
+            break;
         }
     }
 

unreliablefs_errinj.h

@@ -22,6 +22,7 @@
 #define MIN_PROBABLITY 0
 #define MAX_PROBABLITY 100
 #define ERRNO_NOOP -999
+#define ERRNO_1BYTE_READ -998
 #define DEFAULT_SIGNAL_NAME SIGKILL
 
 int error_inject(const char* path, fuse_op operation);

unreliablefs_ops.c

@@ -319,6 +319,8 @@ int unreliable_read(const char *path, char *buf, size_t size, off_t offset,
     int ret = error_inject(path, OP_READ);
     if (ret == -ERRNO_NOOP) {
         return 0;
+    } else if (ret == -ERRNO_1BYTE_READ) {
+        size = 1;
     } else if (ret) {
         return ret;
     }