fuse: add support for kernel writeback cache

- Added kernel-writeback-cache command line and xlator
  option for requesting utilisation of the writeback
  cache of the kernel in FUSE_INIT (see [1]).
- Added attr-times-granularity command line and xlator
  option via which granularity of the {a,m,c}time in
  stat (attr) data that we support can be indicated to
  kernel. This is a means to avoid divergence of the
  attr times between kernel and userspace that could
  occur with writeback-cache, while still maintaining
  maximum time precision the FUSE server is capable of
  (see [2]).
- Handling FATTR_CTIME flag in FUSE_SETATTR that
  indicates presence of ctime in setattr payload.
  Currently we cannot associate arbitrary ctimes to
  files on backend, so we just touch them to update
  their ctimes to current time. Having ctimes in setattr
  payload is also a side effect of writeback cache
  (see [3] and [4]).

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4d99ff8,
     "fuse: Turn writeback cache on"
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e27c9d3,
     "fuse: fuse: add time_gran to INIT_OUT"
[3]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1e18bda,
     "fuse: add .write_inode"
[4]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ab9e13f,
     "fuse: allow ctime flushing to userspace"

Updates: #435
Change-Id: Id174c8e0c815c4456c35f8c53e41a6a507d91855
Signed-off-by: Csaba Henk <csaba@redhat.com>

2 files changed, 72 insertions, 0 deletions

diff --git a/glusterfsd/src/glusterfsd.c b/glusterfsd/src/glusterfsd.c
index b5b8e4d30a7..3de12bc125f 100644
--- a/glusterfsd/src/glusterfsd.c
+++ b/glusterfsd/src/glusterfsd.c
@@ -256,6 +256,11 @@ static struct argp_option gf_options[] = {
          OPTION_ARG_OPTIONAL, "disable/enable fuse event-history"},
         {"reader-thread-count", ARGP_READER_THREAD_COUNT_KEY, "INTEGER",
          OPTION_ARG_OPTIONAL, "set fuse reader thread count"},
+        {"kernel-writeback-cache", ARGP_KERNEL_WRITEBACK_CACHE_KEY, "BOOL",
+         OPTION_ARG_OPTIONAL, "enable fuse in-kernel writeback cache"},
+        {"attr-times-granularity", ARGP_ATTR_TIMES_GRANULARITY_KEY, "NS",
+         OPTION_ARG_OPTIONAL, "declare supported granularity of file attribute"
+         " times in nanoseconds"},
         {0, 0, 0, 0, "Miscellaneous Options:"},
         {0, }
 };
@@ -617,6 +622,44 @@ set_fuse_mount_options (glusterfs_ctx_t *ctx, dict_t *options)
                         goto err;
                 }
         }
+        switch (cmd_args->kernel_writeback_cache) {
+        case GF_OPTION_ENABLE:
+                ret = dict_set_static_ptr(options, "kernel-writeback-cache",
+                        "on");
+                if (ret < 0) {
+                        gf_msg ("glusterfsd", GF_LOG_ERROR, 0, glusterfsd_msg_4,
+                                "failed to set dict value for key "
+                                "kernel-writeback-cache");
+                        goto err;
+                }
+                break;
+        case GF_OPTION_DISABLE:
+                ret = dict_set_static_ptr(options, "kernel-writeback-cache",
+                        "off");
+                if (ret < 0) {
+                        gf_msg ("glusterfsd", GF_LOG_ERROR, 0, glusterfsd_msg_4,
+                                "failed to set dict value for key "
+                                "kernel-writeback-cache");
+                        goto err;
+                }
+                break;
+        case GF_OPTION_DEFERRED: /* default */
+        default:
+                gf_msg_debug ("glusterfsd", 0, "kernel-writeback-cache mode %d",
+                              cmd_args->kernel_writeback_cache);
+                break;
+        }
+        if (cmd_args->attr_times_granularity) {
+                ret = dict_set_uint32 (options, "attr-times-granularity",
+                                       cmd_args->attr_times_granularity);
+                if (ret < 0) {
+                        gf_msg ("glusterfsd", GF_LOG_ERROR, 0, glusterfsd_msg_4,
+                                "failed to set dict value for key "
+                                "attr-times-granularity");
+                        goto err;
+                }
+        }
+
 
         ret = 0;
 err:
@@ -1385,6 +1428,32 @@ no_oom_api:
 
                 break;
 
+        case ARGP_KERNEL_WRITEBACK_CACHE_KEY:
+                if (!arg)
+                        arg = "yes";
+
+                if (gf_string2boolean (arg, &b) == 0) {
+                        cmd_args->kernel_writeback_cache = b;
+
+                        break;
+                }
+
+                argp_failure (state, -1, 0,
+                              "unknown kernel writeback cache setting \"%s\"", arg);
+                break;
+        case ARGP_ATTR_TIMES_GRANULARITY_KEY:
+                if (gf_string2uint32 (arg, &cmd_args->attr_times_granularity)) {
+                        argp_failure (state, -1, 0,
+                                      "unknown attribute times granularity option %s",
+                                      arg);
+                } else if (cmd_args->attr_times_granularity > 1000000000) {
+                        argp_failure (state, -1, 0,
+                                      "Invalid attribute times granularity value %s. "
+                                      "Valid range: [\"0, 1000000000\"]", arg);
+                }
+
+                break;
+
 	}
         return 0;
 }
@@ -1690,6 +1759,7 @@ glusterfs_ctx_defaults_init (glusterfs_ctx_t *ctx)
         cmd_args->fuse_attribute_timeout = -1;
         cmd_args->fuse_entry_timeout = -1;
 	cmd_args->fopen_keep_cache = GF_OPTION_DEFERRED;
+        cmd_args->kernel_writeback_cache = 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 2a03ec09fa2..496a4d95352 100644
--- a/glusterfsd/src/glusterfsd.h
+++ b/glusterfsd/src/glusterfsd.h
@@ -105,6 +105,8 @@ enum argp_option_keys {
         ARGP_PRINT_XLATORDIR_KEY          = 183,
         ARGP_PRINT_STATEDUMPDIR_KEY       = 184,
         ARGP_PRINT_LOGDIR_KEY             = 185,
+        ARGP_KERNEL_WRITEBACK_CACHE_KEY   = 186,
+        ARGP_ATTR_TIMES_GRANULARITY_KEY   = 187,
 };
 
 struct _gfd_vol_top_priv {