fuse: diagnostic FLUSH interrupt

We add dummy interrupt handling for the FLUSH
fuse message. It can be enabled by the
"--fuse-flush-handle-interrupt" hidden command line
option, or "-ofuse-flush-handle-interrupt=yes"
mount option.

It serves no other than diagnostic & demonstational
purposes -- to exercise the interrupt handling framework
a bit and to give an usage example.

Documentation is also provided that showcases interrupt
handling via FLUSH.

Change-Id: I522f1e798501d06b74ac3592a5f73c1ab0590c60
updates: #465
Signed-off-by: Csaba Henk <csaba@redhat.com>

2 files changed, 45 insertions, 0 deletions

diff --git a/glusterfsd/src/glusterfsd.c b/glusterfsd/src/glusterfsd.c
index dfef7922245..f62fbf5e7c4 100644
--- a/glusterfsd/src/glusterfsd.c
+++ b/glusterfsd/src/glusterfsd.c
@@ -264,6 +264,9 @@ static struct argp_option gf_options[] = {
      OPTION_ARG_OPTIONAL,
      "declare supported granularity of file attribute"
      " times in nanoseconds"},
+    {"fuse-flush-handle-interrupt", ARGP_FUSE_FLUSH_HANDLE_INTERRUPT_KEY,
+     "BOOL", OPTION_ARG_OPTIONAL | OPTION_HIDDEN,
+     "handle interrupt in fuse FLUSH handler"},
     {0, 0, 0, 0, "Miscellaneous Options:"},
     {
         0,
@@ -643,6 +646,31 @@ set_fuse_mount_options(glusterfs_ctx_t *ctx, dict_t *options)
             goto err;
         }
     }
+    switch (cmd_args->fuse_flush_handle_interrupt) {
+        case GF_OPTION_ENABLE:
+            ret = dict_set_static_ptr(options, "flush-handle-interrupt", "on");
+            if (ret < 0) {
+                gf_msg("glusterfsd", GF_LOG_ERROR, 0, glusterfsd_msg_4,
+                       "failed to set dict value for key "
+                       "flush-handle-interrupt");
+                goto err;
+            }
+            break;
+        case GF_OPTION_DISABLE:
+            ret = dict_set_static_ptr(options, "flush-handle-interrupt", "off");
+            if (ret < 0) {
+                gf_msg("glusterfsd", GF_LOG_ERROR, 0, glusterfsd_msg_4,
+                       "failed to set dict value for key "
+                       "flush-handle-interrupt");
+                goto err;
+            }
+            break;
+        case GF_OPTION_DEFERRED: /* default */
+        default:
+            gf_msg_debug("glusterfsd", 0, "fuse-flush-handle-interrupt mode %d",
+                         cmd_args->fuse_flush_handle_interrupt);
+            break;
+    }
 
     ret = 0;
 err:
@@ -1421,6 +1449,21 @@ parse_opts(int key, char *arg, struct argp_state *state)
             }
 
             break;
+
+        case ARGP_FUSE_FLUSH_HANDLE_INTERRUPT_KEY:
+            if (!arg)
+                arg = "yes";
+
+            if (gf_string2boolean(arg, &b) == 0) {
+                cmd_args->fuse_flush_handle_interrupt = b;
+
+                break;
+            }
+
+            argp_failure(state, -1, 0,
+                         "unknown fuse flush handle interrupt setting \"%s\"",
+                         arg);
+            break;
     }
     return 0;
 }
@@ -1728,6 +1771,7 @@ glusterfs_ctx_defaults_init(glusterfs_ctx_t *ctx)
     cmd_args->fuse_entry_timeout = -1;
     cmd_args->fopen_keep_cache = GF_OPTION_DEFERRED;
     cmd_args->kernel_writeback_cache = GF_OPTION_DEFERRED;
+    cmd_args->fuse_flush_handle_interrupt = GF_OPTION_DEFERRED;
 
     if (ctx->mem_acct_enable)
         cmd_args->mem_acct = 1;
diff --git a/glusterfsd/src/glusterfsd.h b/glusterfsd/src/glusterfsd.h
index 28d46fc68b9..0042054e138 100644
--- a/glusterfsd/src/glusterfsd.h
+++ b/glusterfsd/src/glusterfsd.h
@@ -108,6 +108,7 @@ enum argp_option_keys {
     ARGP_KERNEL_WRITEBACK_CACHE_KEY = 186,
     ARGP_ATTR_TIMES_GRANULARITY_KEY = 187,
     ARGP_PRINT_LIBEXECDIR_KEY = 188,
+    ARGP_FUSE_FLUSH_HANDLE_INTERRUPT_KEY = 189,
 };
 
 struct _gfd_vol_top_priv {