From 86b0921ac40ad0a34cd4202901efc2f4f774777b Mon Sep 17 00:00:00 2001
From: Or Ozeri <oro@il.ibm.com>
Date: Sun, 6 May 2018 16:10:36 +0300
Subject: [PATCH] enable FUSE read_sync by default

---
 src/s3fs.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/s3fs.cpp b/src/s3fs.cpp
index 4c940b9..5bab8c7 100644
--- a/src/s3fs.cpp
+++ b/src/s3fs.cpp
@@ -120,6 +120,7 @@ static bool nocopyapi             = false;
 static bool norenameapi           = false;
 static bool nonempty              = false;
 static bool allow_other           = false;
+static bool fuse_read_mode_set    = false;
 static bool load_iamrole          = false;
 static uid_t s3fs_uid             = 0;
 static gid_t s3fs_gid             = 0;
@@ -4355,6 +4356,10 @@ static int my_fuse_opt_proc(void* data, const char* arg, int key, struct fuse_ar
       allow_other = true;
       return 1; // continue for fuse option
     }
+    if(0 == strcmp(arg, "sync_read") || 0 == strcmp(arg, "async_read")){
+      fuse_read_mode_set = true;
+      return 1; // continue for fuse option
+    }
     if(0 == STR2NCMP(arg, "mp_umask=")){
       mp_umask = strtol(strchr(arg, '=') + sizeof(char), NULL, 0);
       mp_umask &= (S_IRWXU | S_IRWXG | S_IRWXO);
@@ -4925,6 +4930,15 @@ int main(int argc, char* argv[])
     exit(EXIT_FAILURE);
   }
 
+  // s3fs read is sync (fdent_lock is locked while reading)
+  // FUSE is async read by default
+  // switch FUSE to sync read to avoid hitting FUSE's max_background limit
+  // as well as to make sure that big read requests that are splitted by the kernel
+  // are always read in-order
+  if (!fuse_read_mode_set && 0 != fuse_opt_add_arg(&custom_args, "-osync_read")){
+    exit(EXIT_FAILURE);
+  }
+
   // [NOTE]
   // exclusive option check here.
   //