Fix read/write behavior and return value depending on direct_io

Also add parallel direct write option for 6.2+ kernels.

README.md

@@ -279,6 +279,9 @@ These options are the same regardless of whether you use them with the
   (default: false)
 * **cache.readdir=BOOL**: Cache readdir (if supported by kernel)
   (default: false)
+* **parallel-direct-writes=BOOL**: Allow the kernel to dispatch
+  multiple, parallel (non-extending) write requests for files opened
+  with `direct_io=true` (if supported by the kernel)
 * **direct_io**: deprecated - Bypass page cache. Use `cache.files=off`
   instead. (default: false)
 * **kernel_cache**: deprecated - Do not invalidate data cache on file
@@ -1461,6 +1464,7 @@ understand what behaviors it may impact
 * disable `security_capability` and/or `xattr`
 * increase cache timeouts `cache.attr`, `cache.entry`, `cache.negative_entry`
 * enable (or disable) page caching (`cache.files`)
+* enable `parallel-direct-writes`
 * enable `cache.writeback`
 * enable `cache.statfs`
 * enable `cache.symlinks`

libfuse/include/fuse_common.h

@@ -84,6 +84,8 @@ struct fuse_file_info_t
 
   uint32_t auto_cache : 1;
 
+  uint32_t parallel_direct_writes:1;
+
   /** File handle.  May be filled in by filesystem in open().
       Available in all other file operations */
   uint64_t fh;

libfuse/include/fuse_kernel.h

@@ -197,6 +197,15 @@
  *
  *  7.37
  *  - add FUSE_TMPFILE
+ *
+ *  7.38
+ *  - add FUSE_EXPIRE_ONLY flag to fuse_notify_inval_entry
+ *  - add FOPEN_PARALLEL_DIRECT_WRITES
+ *  - add total_extlen to fuse_in_header
+ *  - add FUSE_MAX_NR_SECCTX
+ *  - add extension header
+ *  - add FUSE_EXT_GROUPS
+ *  - add FUSE_CREATE_SUPP_GROUP
  */
 
 #ifndef _LINUX_FUSE_H
@@ -232,7 +241,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 37
+#define FUSE_KERNEL_MINOR_VERSION 38
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -304,6 +313,7 @@ struct fuse_file_lock {
  * FOPEN_CACHE_DIR: allow caching this directory
  * FOPEN_STREAM: the file is stream-like (no file position at all)
  * FOPEN_NOFLUSH: don't flush data cache on close (unless FUSE_WRITEBACK_CACHE)
+ * FOPEN_PARALLEL_DIRECT_WRITES: Allow concurrent direct writes on the same inode
  */
 #define FOPEN_DIRECT_IO              (1 << 0)
 #define FOPEN_KEEP_CACHE             (1 << 1)
@@ -311,6 +321,7 @@ struct fuse_file_lock {
 #define FOPEN_CACHE_DIR              (1 << 3)
 #define FOPEN_STREAM                 (1 << 4)
 #define FOPEN_NOFLUSH                (1 << 5)
+#define FOPEN_PARALLEL_DIRECT_WRITES (1 << 6)
 
 /**
  * INIT request/reply flags
@@ -356,6 +367,8 @@ struct fuse_file_lock {
  * FUSE_SECURITY_CTX:	add security context to create, mkdir, symlink, and
  *			mknod
  * FUSE_HAS_INODE_DAX:  use per inode DAX
+ * FUSE_CREATE_SUPP_GROUP: add supplementary group info to create, mkdir,
+ *			symlink and mknod (single group that matches parent)
  */
 #define FUSE_ASYNC_READ          (1 << 0)
 #define FUSE_POSIX_LOCKS         (1 << 1)
@@ -392,6 +405,7 @@ struct fuse_file_lock {
 /* bits 32..63 get shifted down 32 bits into the flags2 field */
 #define FUSE_SECURITY_CTX        (1ULL << 32)
 #define FUSE_HAS_INODE_DAX       (1ULL << 33)
+#define FUSE_CREATE_SUPP_GROUP   (1ULL << 34)
 
 /**
  * CUSE INIT request/reply flags
@@ -491,6 +505,23 @@ struct fuse_file_lock {
  */
 #define FUSE_SETXATTR_ACL_KILL_SGID	(1 << 0)
 
+/**
+ * notify_inval_entry flags
+ * FUSE_EXPIRE_ONLY
+ */
+#define FUSE_EXPIRE_ONLY		(1 << 0)
+
+/**
+ * extension type
+ * FUSE_MAX_NR_SECCTX: maximum value of &fuse_secctx_header.nr_secctx
+ * FUSE_EXT_GROUPS: &fuse_supp_groups extension
+ */
+enum fuse_ext_type {
+	/* Types 0..31 are reserved for fuse_secctx_header */
+	FUSE_MAX_NR_SECCTX	= 31,
+	FUSE_EXT_GROUPS		= 32,
+};
+
 enum fuse_opcode {
 	FUSE_LOOKUP		= 1,
 	FUSE_FORGET		= 2,  /* no reply */
@@ -874,7 +905,8 @@ struct fuse_in_header {
 	uint32_t	uid;
 	uint32_t	gid;
 	uint32_t	pid;
-	uint32_t	padding;
+	uint16_t	total_extlen; /* length of extensions in 8byte units */
+	uint16_t	padding;
 };
 
 struct fuse_out_header {
@@ -919,7 +951,7 @@ struct fuse_notify_inval_inode_out {
 struct fuse_notify_inval_entry_out {
 	uint64_t	parent;
 	uint32_t	namelen;
-	uint32_t	padding;
+	uint32_t	flags;
 };
 
 struct fuse_notify_delete_out {
@@ -1035,4 +1067,27 @@ struct fuse_secctx_header {
 	uint32_t	nr_secctx;
 };
 
+/**
+ * struct fuse_ext_header - extension header
+ * @size: total size of this extension including this header
+ * @type: type of extension
+ *
+ * This is made compatible with fuse_secctx_header by using type values >
+ * FUSE_MAX_NR_SECCTX
+ */
+struct fuse_ext_header {
+	uint32_t	size;
+	uint32_t	type;
+};
+
+/**
+ * struct fuse_supp_groups - Supplementary group extension
+ * @nr_groups: number of supplementary groups
+ * @groups: flexible array of group IDs
+ */
+struct fuse_supp_groups {
+	uint32_t	nr_groups;
+	uint32_t	groups[];
+};
+
 #endif /* _LINUX_FUSE_H */

libfuse/lib/fuse_lowlevel.c

@@ -261,18 +261,20 @@ fill_entry(struct fuse_entry_out         *arg,
 
 static
 void
-fill_open(struct fuse_open_out   *arg,
-          const fuse_file_info_t *f)
-{
-  arg->fh = f->fh;
-  if(f->direct_io)
-    arg->open_flags |= FOPEN_DIRECT_IO;
-  if(f->keep_cache)
-    arg->open_flags |= FOPEN_KEEP_CACHE;
-  if(f->nonseekable)
-    arg->open_flags |= FOPEN_NONSEEKABLE;
-  if(f->cache_readdir)
-    arg->open_flags |= FOPEN_CACHE_DIR;
+fill_open(struct fuse_open_out   *arg_,
+          const fuse_file_info_t *ffi_)
+{
+  arg_->fh = ffi_->fh;
+  if(ffi_->direct_io)
+    arg_->open_flags |= FOPEN_DIRECT_IO;
+  if(ffi_->keep_cache)
+    arg_->open_flags |= FOPEN_KEEP_CACHE;
+  if(ffi_->nonseekable)
+    arg_->open_flags |= FOPEN_NONSEEKABLE;
+  if(ffi_->cache_readdir)
+    arg_->open_flags |= FOPEN_CACHE_DIR;
+  if(ffi_->parallel_direct_writes)
+    arg_->open_flags |= FOPEN_PARALLEL_DIRECT_WRITES;
 }
 
 int
@@ -1416,7 +1418,8 @@ fuse_lowlevel_notify_inval_entry(struct fuse_chan *ch,
 
   outarg.parent  = parent;
   outarg.namelen = namelen;
-  outarg.padding = 0;
+  // TODO: Add ability to set `flags`
+  outarg.flags   = 0;
 
   iov[1].iov_base = &outarg;
   iov[1].iov_len = sizeof(outarg);

man/mergerfs.1

@@ -377,6 +377,10 @@ to enable page caching for when \f[C]cache.files=per-process\f[R].
 \f[B]cache.readdir=BOOL\f[R]: Cache readdir (if supported by kernel)
 (default: false)
 .IP \[bu] 2
+\f[B]parallel-direct-writes=BOOL\f[R]: Allow the kernel to dispatch
+multiple, parallel (non-extending) write requests for files opened with
+\f[C]direct_io=true\f[R] (if supported by the kernel)
+.IP \[bu] 2
 \f[B]direct_io\f[R]: deprecated - Bypass page cache.
 Use \f[C]cache.files=off\f[R] instead.
 (default: false)
@@ -1902,6 +1906,8 @@ increase cache timeouts \f[C]cache.attr\f[R], \f[C]cache.entry\f[R],
 .IP \[bu] 2
 enable (or disable) page caching (\f[C]cache.files\f[R])
 .IP \[bu] 2
+enable \f[C]parallel-direct-writes\f[R]
+.IP \[bu] 2
 enable \f[C]cache.writeback\f[R]
 .IP \[bu] 2
 enable \f[C]cache.statfs\f[R]

src/config.cpp

@@ -107,6 +107,7 @@ Config::Config()
     moveonenospc(false),
     nfsopenhack(NFSOpenHack::ENUM::OFF),
     nullrw(false),
+    parallel_direct_writes(false),
     pid(::getpid()),
     posix_acl(false),
     readahead(0),
@@ -182,6 +183,7 @@ Config::Config()
   _map["nfsopenhack"]            = &nfsopenhack;
   _map["nullrw"]                 = &nullrw;
   _map["pid"]                    = &pid;
+  _map["parallel-direct-writes"] = &parallel_direct_writes;
   _map["pin-threads"]            = &fuse_pin_threads;
   _map["posix_acl"]              = &posix_acl;
   _map["readahead"]              = &readahead;

src/config.hpp

@@ -131,6 +131,7 @@ public:
   MoveOnENOSPC   moveonenospc;
   NFSOpenHack    nfsopenhack;
   ConfigBOOL     nullrw;
+  ConfigBOOL     parallel_direct_writes;
   ConfigUINT64   pid;
   ConfigBOOL     posix_acl;
   ConfigUINT64   readahead;
@@ -151,7 +152,6 @@ public:
   ConfigBOOL     writeback_cache;
   XAttr          xattr;
 
-
 private:
   bool _initialized;
 

src/fileinfo.hpp

@@ -18,19 +18,25 @@
 
 #include "fh.hpp"
 
+#include <cstdint>
 #include <string>
+#include <mutex>
 
 
 class FileInfo : public FH
 {
 public:
-  FileInfo(const int   fd_,
-           const char *fusepath_)
+  FileInfo(int const   fd_,
+           char const *fusepath_,
+           bool const  direct_io_)
     : FH(fusepath_),
-      fd(fd_)
+      fd(fd_),
+      direct_io(direct_io_)
   {
   }
 
 public:
   int fd;
+  uint32_t direct_io:1;
+  std::mutex mutex;
 };

src/fs_copydata_readwrite.cpp

@@ -65,11 +65,9 @@ namespace l
     size_t  totalwritten;
     vector<char> buf;
 
-    bufsize = (128 * 1024);
+    bufsize = (1024 * 1024);
     buf.resize(bufsize);
 
-    fs::lseek(src_fd_,0,SEEK_SET);
-
     totalwritten = 0;
     while(totalwritten < count_)
       {

src/fs_dup2.hpp

@@ -0,0 +1,38 @@
+/*
+  ISC License
+
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+#include <unistd.h>
+
+
+namespace fs
+{
+  static
+  inline
+  int
+  dup2(int const oldfd_,
+       int const newfd_)
+  {
+    int rv;
+
+    rv = ::dup2(oldfd_,newfd_);
+
+    return ((rv == -1) ? -errno : rv);
+  }
+}

src/fs_movefile.cpp

@@ -156,8 +156,6 @@ namespace l
 
     fs::unlink(srcfd_filepath);
 
-    fs::close(origfd_);
-
     return rv;
   }
 }

src/fs_preadn.hpp

@@ -0,0 +1,59 @@
+/*
+  ISC License
+
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+#include "fs_pread.hpp"
+
+
+namespace fs
+{
+  static
+  inline
+  ssize_t
+  preadn(int const     fd_,
+         void         *buf_,
+         size_t const  count_,
+         off_t const   offset_,
+         int          *err_)
+  {
+    ssize_t rv;
+    ssize_t count = count_;
+    off_t   offset = offset_;
+    char const *buf = (char const *)buf_;
+
+    *err_ = 0;
+    while(count > 0)
+      {
+        rv = fs::pread(fd_,buf,count,offset);
+        if(rv == 0)
+          return (count_ - count);
+        if(rv < 0)
+          {
+            *err_ = rv;
+            return (count_ - count);
+          }
+
+        buf    += rv;
+        count  -= rv;
+        offset += rv;
+      }
+
+    return count_;
+  }
+}

src/fs_pwrite.hpp

@@ -0,0 +1,42 @@
+/*
+  ISC License
+
+  Copyright (c) 2016, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+#include <unistd.h>
+
+
+namespace fs
+{
+  static
+  inline
+  ssize_t
+  pwrite(int const     fd_,
+         void const   *buf_,
+         size_t const  count_,
+         off_t const   offset_)
+  {
+    ssize_t rv;
+
+    rv = ::pwrite(fd_,buf_,count_,offset_);
+    if(rv == -1)
+      return -errno;
+
+    return rv;
+  }
+}

src/fs_pwriten.hpp

@@ -0,0 +1,59 @@
+/*
+  ISC License
+
+  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#pragma once
+
+#include "fs_pwrite.hpp"
+
+
+namespace fs
+{
+  static
+  inline
+  ssize_t
+  pwriten(const int     fd_,
+          const void   *buf_,
+          const size_t  count_,
+          const off_t   offset_,
+          int          *err_)
+  {
+    ssize_t rv;
+    ssize_t count  = count_;
+    off_t   offset = offset_;
+    char const *buf = (char const *)buf_;
+
+    *err_ = 0;
+    while(count > 0)
+      {
+        rv = fs::pwrite(fd_,buf,count,offset);
+        if(rv == 0)
+          return (count_ - count);
+        if(rv < 0)
+          {
+            *err_ = rv;
+            return (count_ - count);
+          }
+
+        buf    += rv;
+        count  -= rv;
+        offset += rv;
+      }
+
+    return count_;
+  }
+}

src/fs_write.hpp

@@ -32,15 +32,4 @@ namespace fs
   {
     return ::write(fd_,buf_,count_);
   }
-
-  static
-  inline
-  ssize_t
-  pwrite(const int     fd_,
-         const void   *buf_,
-         const size_t  count_,
-         const off_t   offset_)
-  {
-    return ::pwrite(fd_,buf_,count_,offset_);
-  }
 }

src/fuse_create.cpp

@@ -102,6 +102,9 @@ namespace l
           }
         break;
       }
+
+    if(cfg_->parallel_direct_writes == true)
+      ffi_->parallel_direct_writes = ffi_->direct_io;
   }
 
   static
@@ -121,21 +124,23 @@ namespace l
   int
   create_core(const std::string &createpath_,
               const char        *fusepath_,
+              fuse_file_info_t  *ffi_,
               const mode_t       mode_,
-              const mode_t       umask_,
-              const int          flags_,
-              uint64_t          *fh_)
+              const mode_t       umask_)
   {
     int rv;
+    FileInfo *fi;
     std::string fullpath;
 
     fullpath = fs::path::make(createpath_,fusepath_);
 
-    rv = l::create_core(fullpath,mode_,umask_,flags_);
+    rv = l::create_core(fullpath,mode_,umask_,ffi_->flags);
     if(rv == -1)
       return -errno;
 
-    *fh_ = reinterpret_cast<uint64_t>(new FileInfo(rv,fusepath_));
+    fi = new FileInfo(rv,fusepath_,ffi_->direct_io);
+
+    ffi_->fh = reinterpret_cast<uint64_t>(fi);
 
     return 0;
   }
@@ -146,10 +151,9 @@ namespace l
          const Policy::Create &createFunc_,
          const Branches       &branches_,
          const char           *fusepath_,
+         fuse_file_info_t     *ffi_,
          const mode_t          mode_,
-         const mode_t          umask_,
-         const int             flags_,
-         uint64_t             *fh_)
+         const mode_t          umask_)
   {
     int rv;
     std::string fullpath;
@@ -173,10 +177,9 @@ namespace l
 
     return l::create_core(createpaths[0],
                           fusepath_,
+                          ffi_,
                           mode_,
-                          umask_,
-                          flags_,
-                          fh_);
+                          umask_);
   }
 }
 
@@ -187,6 +190,7 @@ namespace FUSE
          mode_t            mode_,
          fuse_file_info_t *ffi_)
   {
+    int rv;
     Config::Read cfg;
     const fuse_context *fc = fuse_get_context();
     const ugid::Set     ugid(fc->uid,fc->gid);
@@ -196,13 +200,14 @@ namespace FUSE
     if(cfg->writeback_cache)
       l::tweak_flags_writeback_cache(&ffi_->flags);
 
-    return l::create(cfg->func.getattr.policy,
+    rv = l::create(cfg->func.getattr.policy,
                    cfg->func.create.policy,
                    cfg->branches,
                    fusepath_,
+                   ffi_,
                    mode_,
-                     fc->umask,
-                     ffi_->flags,
-                     &ffi_->fh);
+                   fc->umask);
+
+    return rv;
   }
 }

src/fuse_open.cpp

@@ -165,32 +165,37 @@ namespace l
           }
         break;
       }
+
+    if(cfg_->parallel_direct_writes == true)
+      ffi_->parallel_direct_writes = ffi_->direct_io;
   }
 
   static
   int
   open_core(const std::string &basepath_,
             const char        *fusepath_,
-            const int          flags_,
+            fuse_file_info_t  *ffi_,
             const bool         link_cow_,
-            const NFSOpenHack  nfsopenhack_,
-            uint64_t          *fh_)
+            const NFSOpenHack  nfsopenhack_)
   {
     int fd;
+    FileInfo *fi;
     std::string fullpath;
 
     fullpath = fs::path::make(basepath_,fusepath_);
 
-    if(link_cow_ && fs::cow::is_eligible(fullpath.c_str(),flags_))
+    if(link_cow_ && fs::cow::is_eligible(fullpath.c_str(),ffi_->flags))
       fs::cow::break_link(fullpath.c_str());
 
-    fd = fs::open(fullpath,flags_);
+    fd = fs::open(fullpath,ffi_->flags);
     if((fd == -1) && (errno == EACCES))
-      fd = l::nfsopenhack(fullpath,flags_,nfsopenhack_);
+      fd = l::nfsopenhack(fullpath,ffi_->flags,nfsopenhack_);
     if(fd == -1)
       return -errno;
 
-    *fh_ = reinterpret_cast<uint64_t>(new FileInfo(fd,fusepath_));
+    fi = new FileInfo(fd,fusepath_,ffi_->direct_io);
+
+    ffi_->fh = reinterpret_cast<uint64_t>(fi);
 
     return 0;
   }
@@ -200,10 +205,9 @@ namespace l
   open(const Policy::Search &searchFunc_,
        const Branches       &branches_,
        const char           *fusepath_,
-       const int             flags_,
+       fuse_file_info_t     *ffi_,
        const bool            link_cow_,
-       const NFSOpenHack     nfsopenhack_,
-       uint64_t             *fh_)
+       const NFSOpenHack     nfsopenhack_)
   {
     int rv;
     StrVec basepaths;
@@ -212,7 +216,7 @@ namespace l
     if(rv == -1)
       return -errno;
 
-    return l::open_core(basepaths[0],fusepath_,flags_,link_cow_,nfsopenhack_,fh_);
+    return l::open_core(basepaths[0],fusepath_,ffi_,link_cow_,nfsopenhack_);
   }
 }
 
@@ -222,6 +226,7 @@ namespace FUSE
   open(const char       *fusepath_,
        fuse_file_info_t *ffi_)
   {
+    int rv;
     Config::Read cfg;
     const fuse_context *fc  = fuse_get_context();
     const ugid::Set     ugid(fc->uid,fc->gid);
@@ -231,12 +236,13 @@ namespace FUSE
     if(cfg->writeback_cache)
       l::tweak_flags_writeback_cache(&ffi_->flags);
 
-    return l::open(cfg->func.open.policy,
+    rv = l::open(cfg->func.open.policy,
                  cfg->branches,
                  fusepath_,
-                   ffi_->flags,
+                 ffi_,
                  cfg->link_cow,
-                   cfg->nfsopenhack,
-                   &ffi_->fh);
+                 cfg->nfsopenhack);
+
+    return rv;
   }
 }

src/fuse_read.cpp

@@ -23,14 +23,26 @@
 #include <stdlib.h>
 #include <string.h>
 
-typedef struct fuse_bufvec fuse_bufvec;
-
 
 namespace l
 {
   static
   int
-  read(const int     fd_,
+  read_direct_io(const int     fd_,
+                 char         *buf_,
+                 const size_t  size_,
+                 const off_t   offset_)
+  {
+    int rv;
+
+    rv = fs::pread(fd_,buf_,size_,offset_);
+
+    return rv;
+  }
+
+  static
+  int
+  read_cached(const int     fd_,
               char         *buf_,
               const size_t  size_,
               const off_t   offset_)
@@ -53,10 +65,10 @@ namespace FUSE
   {
     FileInfo *fi = reinterpret_cast<FileInfo*>(ffi_->fh);
 
-    return l::read(fi->fd,
-                   buf_,
-                   size_,
-                   offset_);
+    if(fi->direct_io)
+      return l::read_direct_io(fi->fd,buf_,size_,offset_);
+
+    return l::read_cached(fi->fd,buf_,size_,offset_);
   }
 
   int

src/fuse_write.cpp

@@ -17,8 +17,11 @@
 #include "config.hpp"
 #include "errno.hpp"
 #include "fileinfo.hpp"
+#include "fs_close.hpp"
+#include "fs_dup2.hpp"
 #include "fs_movefile.hpp"
-#include "fs_write.hpp"
+#include "fs_pwrite.hpp"
+#include "fs_pwriten.hpp"
 #include "ugid.hpp"
 
 #include "fuse.h"
@@ -36,37 +39,53 @@ namespace l
 {
   static
   bool
-  out_of_space(const int error_)
+  out_of_space(const ssize_t error_)
   {
-    return ((error_ == ENOSPC) ||
-            (error_ == EDQUOT));
+    return ((error_ == -ENOSPC) ||
+            (error_ == -EDQUOT));
   }
 
   static
   int
-  write(const int     fd_,
-        const void   *buf_,
+  move_and_pwrite(const char   *buf_,
                   const size_t  count_,
-        const off_t   offset_)
+                  const off_t   offset_,
+                  FileInfo     *fi_,
+                  int           err_)
   {
-    int rv;
+    int err;
+    ssize_t rv;
+    Config::Read cfg;
 
-    rv = fs::pwrite(fd_,buf_,count_,offset_);
-    if(rv == -1)
-      return -errno;
+    if(cfg->moveonenospc.enabled == false)
+      return err_;
 
-    return rv;
+    rv = fs::movefile_as_root(cfg->moveonenospc.policy,
+                              cfg->branches,
+                              fi_->fusepath,
+                              fi_->fd);
+    if(rv < 0)
+      return err_;
+
+    err = fs::dup2(rv,fi_->fd);
+    fs::close(rv);
+    if(err < 0)
+      return err;
+
+    return fs::pwrite(fi_->fd,buf_,count_,offset_);
   }
 
   static
   int
-  move_and_write(const char   *buf_,
-                 const size_t  count_,
-                 const off_t   offset_,
+  move_and_pwriten(char const    *buf_,
+                   size_t const   count_,
+                   off_t const    offset_,
                    FileInfo      *fi_,
-                 int           err_)
+                   ssize_t const  err_,
+                   ssize_t const  written_)
   {
-    int rv;
+    int err;
+    ssize_t rv;
     Config::Read cfg;
 
     if(cfg->moveonenospc.enabled == false)
@@ -79,9 +98,70 @@ namespace l
     if(rv < 0)
       return err_;
 
-    fi_->fd = rv;
+    err = fs::dup2(rv,fi_->fd);
+    fs::close(rv);
+    if(err < 0)
+      return err;
+
+    rv = fs::pwriten(fi_->fd,
+                     buf_ + written_,
+                     count_ - written_,
+                     offset_ + written_,
+                     &err);
+    if(err < 0)
+      return err;
+
+    return (rv + written_);
+  }
+
+  // When in direct_io mode write's return value should match that of
+  // the operation.
+  // 0 on EOF
+  // N bytes written (short writes included)
+  // -errno on error
+  // See libfuse/include/fuse.h for more details
+  static
+  int
+  write_direct_io(const char   *buf_,
+                  const size_t  count_,
+                  const off_t   offset_,
+                  FileInfo     *fi_)
+  {
+    ssize_t rv;
+
+    rv = fs::pwrite(fi_->fd,buf_,count_,offset_);
+    if(l::out_of_space(rv))
+      rv = l::move_and_pwrite(buf_,count_,offset_,fi_,rv);
+
+    return rv;
+  }
+
+  // When not in direct_io mode write's return value is more complex.
+  // 0 or less than `count` on EOF
+  // `count` on non-errors
+  // -errno on error
+  // See libfuse/include/fuse.h for more details
+  static
+  int
+  write_cached(const char   *buf_,
+               const size_t  count_,
+               const off_t   offset_,
+               FileInfo     *fi_)
+  {
+    int err;
+    ssize_t rv;
 
-    return l::write(fi_->fd,buf_,count_,offset_);
+    rv = fs::pwriten(fi_->fd,buf_,count_,offset_,&err);
+    if(rv == (ssize_t)count_)
+      return count_;
+    if(rv == 0)
+      return 0;
+    if(err && !l::out_of_space(err))
+      return err;
+
+    rv = l::move_and_pwriten(buf_,count_,offset_,fi_,err,rv);
+
+    return rv;
   }
 
   static
@@ -91,16 +171,25 @@ namespace l
         const size_t            count_,
         const off_t             offset_)
   {
-    int rv;
-    FileInfo* fi;
+    FileInfo *fi;
 
     fi = reinterpret_cast<FileInfo*>(ffi_->fh);
 
-    rv = l::write(fi->fd,buf_,count_,offset_);
-    if(l::out_of_space(-rv))
-      rv = l::move_and_write(buf_,count_,offset_,fi,rv);
-
-    return rv;
+    // Concurrent writes can only happen if:
+    // 1) writeback-cache is enabled and using page caching
+    // 2) parallel_direct_writes is enabled and file has `direct_io=true`
+    // Will look into selectively locking in the future
+    // A reader/writer lock would probably be the best option given
+    // the expense of the write itself in comparison. Alternatively,
+    // could change the move file behavior to use a known target file
+    // and have threads use O_EXCL and back off and wait for the
+    // transfer to complete before retrying.
+    std::lock_guard<std::mutex> guard(fi->mutex);
+
+    if(fi->direct_io)
+      return l::write_direct_io(buf_,count_,offset_,fi);
+
+    return l::write_cached(buf_,count_,offset_,fi);
   }
 }