Merge pull request #509 from trapexit/cow

add link_cow feature

README.md

@@ -1,6 +1,6 @@
 % mergerfs(1) mergerfs user manual
 % Antonio SJ Musumeci <trapexit@spawn.link>
-% 2018-09-30
+% 2018-10-05
 
 # NAME
 
@@ -72,6 +72,7 @@ mergerfs does **not** support the copy-on-write (CoW) behavior found in **aufs**
 * **nullrw=true|false**: turns reads and writes into no-ops. The request will succeed but do nothing. Useful for benchmarking mergerfs. (default: false)
 * **ignorepponrename=true|false**: ignore path preserving on rename. Typically rename and link act differently depending on the policy of `create` (read below). Enabling this will cause rename and link to always use the non-path preserving behavior. This means files, when renamed or linked, will stay on the same drive. (default: false)
 * **security_capability=true|false**: If false return ENOATTR when xattr security.capability is queried. (default: true)
+* **link_cow=true|false**: When enabled if a regular file is opened which has a link count > 1 it will copy the file to a temporary file and rename over the original. Breaking the link and providing a basic copy-on-write function similar to cow-shell. (default: false)
 * **threads=num**: number of threads to use in multithreaded mode. When set to zero (the default) it will attempt to discover and use the number of logical cores. If the lookup fails it will fall back to using 4. If the thread count is set negative it will look up the number of cores then divide by the absolute value. ie. threads=-2 on an 8 core machine will result in 8 / 2 = 4 threads. There will always be at least 1 thread. NOTE: higher number of threads increases parallelism but usually decreases throughput. (default: number of cores) *NOTE2:* the option is unavailable when built with system libfuse.
 * **fsname=name**: sets the name of the filesystem as seen in **mount**, **df**, etc. Defaults to a list of the source paths concatenated together with the longest common prefix removed.
 * **func.&lt;func&gt;=&lt;policy&gt;**: sets the specific FUSE function's policy. See below for the list of value types. Example: **func.getattr=newest**
@@ -646,6 +647,10 @@ See the previous question's answer.
 
 Yes. You need to use `use_ino` to support proper reporting of inodes. Read the section "rename & link" for caveats.
 
+#### Does mergerfs support CoW / copy-on-write?
+
+Not in the sense of a filesystem like BTRFS or ZFS nor in the overlayfs or aufs sense. It does offer a [cow-shell](http://manpages.ubuntu.com/manpages/bionic/man1/cow-shell.1.html) like hardlink breaking (copy to temp file then rename over original) which can be useful when wanting to save space by hardlinking duplicate files but wish to treat each name as if it were a unique and separate file.
+
 #### Why can't I see my files / directories?
 
 It's almost always a permissions issue. Unlike mhddfs, which runs as root and attempts to access content as such, mergerfs always changes it's credentials to that of the caller. This means that if the user does not have access to a file or directory than neither will mergerfs. However, because mergerfs is creating a union of paths it may be able to read some files and directories on one drive but not another resulting in an incomplete set.

man/mergerfs.1

@@ -1,7 +1,7 @@
 .\"t
 .\" Automatically generated by Pandoc 1.19.2.4
 .\"
-.TH "mergerfs" "1" "2018\-09\-30" "mergerfs user manual" ""
+.TH "mergerfs" "1" "2018\-10\-05" "mergerfs user manual" ""
 .hy
 .SH NAME
 .PP
@@ -156,6 +156,13 @@ This means files, when renamed or linked, will stay on the same drive.
 xattr security.capability is queried.
 (default: true)
 .IP \[bu] 2
+\f[B]link_cow=true|false\f[]: When enabled if a regular file is opened
+which has a link count > 1 it will copy the file to a temporary file and
+rename over the original.
+Breaking the link and providing a basic copy\-on\-write function similar
+to cow\-shell.
+(default: false)
+.IP \[bu] 2
 \f[B]threads=num\f[]: number of threads to use in multithreaded mode.
 When set to zero (the default) it will attempt to discover and use the
 number of logical cores.
@@ -1361,6 +1368,16 @@ See the previous question\[aq]s answer.
 Yes.
 You need to use \f[C]use_ino\f[] to support proper reporting of inodes.
 Read the section "rename & link" for caveats.
+.SS Does mergerfs support CoW / copy\-on\-write?
+.PP
+Not in the sense of a filesystem like BTRFS or ZFS nor in the overlayfs
+or aufs sense.
+It does offer a
+cow\-shell (http://manpages.ubuntu.com/manpages/bionic/man1/cow-shell.1.html)
+like hardlink breaking (copy to temp file then rename over original)
+which can be useful when wanting to save space by hardlinking duplicate
+files but wish to treat each name as if it were a unique and separate
+file.
 .SS Why can\[aq]t I see my files / directories?
 .PP
 It\[aq]s almost always a permissions issue.

src/config.cpp

@@ -46,6 +46,7 @@ namespace mergerfs
       nullrw(false),
       ignorepponrename(false),
       security_capability(true),
+      link_cow(false),
       POLICYINIT(access),
       POLICYINIT(chmod),
       POLICYINIT(chown),

src/config.hpp

@@ -16,17 +16,17 @@
 
 #pragma once
 
+#include "fusefunc.hpp"
+#include "policy.hpp"
+
 #include <fuse.h>
 
-#include <sys/stat.h>
 #include <stdint.h>
+#include <sys/stat.h>
 
 #include <string>
 #include <vector>
 
-#include "policy.hpp"
-#include "fusefunc.hpp"
-
 namespace mergerfs
 {
   class Config
@@ -37,8 +37,8 @@ namespace mergerfs
   public:
     int set_func_policy(const std::string &fusefunc_,
                         const std::string &policy_);
-    int set_category_policy(const std::string &category,
-                            const std::string &policy);
+    int set_category_policy(const std::string &category_,
+                            const std::string &policy_);
 
   public:
     std::string              destmount;
@@ -53,6 +53,7 @@ namespace mergerfs
     bool                     nullrw;
     bool                     ignorepponrename;
     bool                     security_capability;
+    bool                     link_cow;
 
   public:
     const Policy  *policies[FuseFunc::Enum::END];

src/fs_base_open.hpp

@@ -18,30 +18,49 @@
 
 #pragma once
 
-#include <string>
-
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
+#include <string>
+
 namespace fs
 {
   static
   inline
   int
-  open(const std::string &path,
-       const int          flags)
+  open(const char *path_,
+       const int   flags_)
+  {
+    return ::open(path_,flags_);
+  }
+
+  static
+  inline
+  int
+  open(const char   *path_,
+       const int     flags_,
+       const mode_t  mode_)
+  {
+    return ::open(path_,flags_,mode_);
+  }
+
+  static
+  inline
+  int
+  open(const std::string &path_,
+       const int          flags_)
   {
-    return ::open(path.c_str(),flags);
+    return fs::open(path_.c_str(),flags_);
   }
 
   static
   inline
   int
-  open(const std::string &path,
-       const int          flags,
-       const mode_t       mode)
+  open(const std::string &path_,
+       const int          flags_,
+       const mode_t       mode_)
   {
-    return ::open(path.c_str(),flags,mode);
+    return fs::open(path_.c_str(),flags_,mode_);
   }
 }

src/fs_base_rename.hpp

@@ -25,9 +25,18 @@ namespace fs
   static
   inline
   int
-  rename(const std::string &oldpath,
-         const std::string &newpath)
+  rename(const char *oldpath_,
+         const char *newpath_)
   {
-    return ::rename(oldpath.c_str(),newpath.c_str());
+    return ::rename(oldpath_,newpath_);
+  }
+
+  static
+  inline
+  int
+  rename(const std::string &oldpath_,
+         const std::string &newpath_)
+  {
+    return fs::rename(oldpath_.c_str(),newpath_.c_str());
   }
 }

src/fs_base_unlink.hpp

@@ -27,8 +27,16 @@ namespace fs
   static
   inline
   int
-  unlink(const std::string &path)
+  unlink(const char *path_)
   {
-    return ::unlink(path.c_str());
+    return ::unlink(path_);
+  }
+
+  static
+  inline
+  int
+  unlink(const std::string &path_)
+  {
+    return fs::unlink(path_.c_str());
   }
 }

src/fs_clonefile.cpp

@@ -14,12 +14,6 @@
   OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
 
-#include <fcntl.h>
-#include <stdlib.h>
-
-#include <string>
-#include <vector>
-
 #include "errno.hpp"
 #include "fs_attr.hpp"
 #include "fs_base_chmod.hpp"
@@ -37,6 +31,12 @@
 #include "fs_sendfile.hpp"
 #include "fs_xattr.hpp"
 
+#include <fcntl.h>
+#include <stdlib.h>
+
+#include <string>
+#include <vector>
+
 #ifndef O_LARGEFILE
 # define O_LARGEFILE 0
 #endif
@@ -49,36 +49,36 @@ using std::string;
 using std::vector;
 
 int
-writen(const int     fd,
-       const char   *buf,
-       const size_t  count)
+writen(const int     fd_,
+       const char   *buf_,
+       const size_t  count_)
 {
   size_t nleft;
   ssize_t nwritten;
 
-  nleft = count;
+  nleft = count_;
   do
     {
-      nwritten = fs::write(fd,buf,nleft);
+      nwritten = fs::write(fd_,buf_,nleft);
       if((nwritten == -1) && (errno == EINTR))
         continue;
       if(nwritten == -1)
         return -1;
 
       nleft -= nwritten;
-      buf   += nwritten;
+      buf_  += nwritten;
     }
   while(nleft > 0);
 
-  return count;
+  return count_;
 }
 
 static
 int
-copyfile_rw(const int    fdin,
-            const int    fdout,
-            const size_t count,
-            const size_t blocksize)
+copyfile_rw(const int    src_fd_,
+            const int    dst_fd_,
+            const size_t count_,
+            const size_t blocksize_)
 {
   ssize_t nr;
   ssize_t nw;
@@ -86,15 +86,15 @@ copyfile_rw(const int    fdin,
   size_t  totalwritten;
   vector<char> buf;
 
-  bufsize = (blocksize * 16);
+  bufsize = (blocksize_ * 16);
   buf.resize(bufsize);
 
-  fs::lseek(fdin,0,SEEK_SET);
+  fs::lseek(src_fd_,0,SEEK_SET);
 
   totalwritten = 0;
-  while(totalwritten < count)
+  while(totalwritten < count_)
     {
-      nr = fs::read(fdin,&buf[0],bufsize);
+      nr = fs::read(src_fd_,&buf[0],bufsize);
       if(nr == 0)
         return totalwritten;
       if((nr == -1) && (errno == EINTR))
@@ -102,7 +102,7 @@ copyfile_rw(const int    fdin,
       if(nr == -1)
         return -1;
 
-      nw = writen(fdout,&buf[0],nr);
+      nw = writen(dst_fd_,&buf[0],nr);
       if(nw == -1)
         return -1;
 
@@ -114,30 +114,30 @@ copyfile_rw(const int    fdin,
 
 static
 int
-copydata(const int    fdin,
-         const int    fdout,
-         const size_t count,
-         const size_t blocksize)
+copydata(const int    src_fd_,
+         const int    dst_fd_,
+         const size_t count_,
+         const size_t blocksize_)
 {
   int rv;
 
-  fs::fadvise_willneed(fdin,0,count);
-  fs::fadvise_sequential(fdin,0,count);
+  fs::fadvise_willneed(src_fd_,0,count_);
+  fs::fadvise_sequential(src_fd_,0,count_);
 
-  fs::fallocate(fdout,0,0,count);
+  fs::fallocate(dst_fd_,0,0,count_);
 
-  rv = fs::sendfile(fdin,fdout,count);
+  rv = fs::sendfile(src_fd_,dst_fd_,count_);
   if((rv == -1) && ((errno == EINVAL) || (errno == ENOSYS)))
-    return ::copyfile_rw(fdin,fdout,count,blocksize);
+    return ::copyfile_rw(src_fd_,dst_fd_,count_,blocksize_);
 
   return rv;
 }
 
 static
 bool
-ignorable_error(const int err)
+ignorable_error(const int err_)
 {
-  switch(err)
+  switch(err_)
     {
     case ENOTTY:
     case ENOTSUP:
@@ -153,69 +153,40 @@ ignorable_error(const int err)
 namespace fs
 {
   int
-  clonefile(const int fdin,
-            const int fdout)
+  clonefile(const int src_fd_,
+            const int dst_fd_)
   {
     int rv;
-    struct stat stin;
+    struct stat src_st;
 
-    rv = fs::fstat(fdin,stin);
+    rv = fs::fstat(src_fd_,src_st);
     if(rv == -1)
       return -1;
 
-    rv = ::copydata(fdin,fdout,stin.st_size,stin.st_blksize);
+    rv = ::copydata(src_fd_,dst_fd_,src_st.st_size,src_st.st_blksize);
     if(rv == -1)
       return -1;
 
-    rv = fs::attr::copy(fdin,fdout);
+    rv = fs::attr::copy(src_fd_,dst_fd_);
     if((rv == -1) && !ignorable_error(errno))
       return -1;
 
-    rv = fs::xattr::copy(fdin,fdout);
+    rv = fs::xattr::copy(src_fd_,dst_fd_);
     if((rv == -1) && !ignorable_error(errno))
       return -1;
 
-    rv = fs::fchown_check_on_error(fdout,stin);
+    rv = fs::fchown_check_on_error(dst_fd_,src_st);
     if(rv == -1)
       return -1;
 
-    rv = fs::fchmod_check_on_error(fdout,stin);
+    rv = fs::fchmod_check_on_error(dst_fd_,src_st);
     if(rv == -1)
       return -1;
 
-    rv = fs::utime(fdout,stin);
+    rv = fs::utime(dst_fd_,src_st);
     if(rv == -1)
       return -1;
 
     return 0;
   }
-
-  int
-  clonefile(const string &in,
-            const string &out)
-  {
-    int rv;
-    int fdin;
-    int fdout;
-    int error;
-
-    fdin = fs::open(in,O_RDONLY|O_NOFOLLOW);
-    if(fdin == -1)
-      return -1;
-
-    const int    flags = O_CREAT|O_LARGEFILE|O_NOATIME|O_NOFOLLOW|O_TRUNC|O_WRONLY;
-    const mode_t mode  = S_IWUSR;
-    fdout = fs::open(out,flags,mode);
-    if(fdout == -1)
-      return -1;
-
-    rv = fs::clonefile(fdin,fdout);
-    error = errno;
-
-    fs::close(fdin);
-    fs::close(fdout);
-
-    errno = error;
-    return rv;
-  }
 }

src/fs_clonefile.hpp

@@ -16,12 +16,9 @@
 
 #pragma once
 
-#include <string>
-
 namespace fs
 {
-  int clonefile(const int fdin,
-                const int fdout);
-  int clonefile(const std::string &from,
-                const std::string &to);
+  int
+  clonefile(const int src_fd_,
+            const int dst_fd_);
 }

src/fs_cow.cpp

@@ -0,0 +1,118 @@
+/*
+  ISC License
+
+  Copyright (c) 2018, 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.
+*/
+
+#include "fs_clonefile.hpp"
+#include "fs_mktemp.hpp"
+
+#include "fs_base_close.hpp"
+#include "fs_base_open.hpp"
+#include "fs_base_rename.hpp"
+#include "fs_base_stat.hpp"
+#include "fs_base_unlink.hpp"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <string>
+
+using std::string;
+
+static
+int
+cleanup_on_error(const int     src_fd_,
+                 const int     dst_fd_       = -1,
+                 const string &dst_fullpath_ = string())
+{
+  int error = errno;
+
+  if(src_fd_ >= 0)
+    fs::close(src_fd_);
+  if(dst_fd_ >= 0)
+    fs::close(dst_fd_);
+  if(!dst_fullpath_.empty())
+    fs::unlink(dst_fullpath_);
+
+  errno = error;
+
+  return -1;
+}
+
+
+namespace fs
+{
+  namespace cow
+  {
+    bool
+    is_eligible(const int          flags_,
+                const struct stat &st_)
+    {
+      return (((flags_ & O_RDWR) || (flags_ & O_WRONLY))  &&
+              (S_ISREG(st_.st_mode))                      &&
+              (st_.st_nlink > 1));
+    }
+
+    bool
+    is_eligible(const char *fullpath_,
+                const int   flags_)
+    {
+      int rv;
+      struct stat st;
+
+      rv = fs::stat(fullpath_,st);
+      if(rv == -1)
+        return false;
+
+      return fs::cow::is_eligible(flags_,st);
+    }
+
+    int
+    break_link(const char *src_fullpath_)
+    {
+      int rv;
+      int src_fd;
+      int dst_fd;
+      string dst_fullpath;
+
+      src_fd = fs::open(src_fullpath_,O_RDONLY|O_NOFOLLOW|O_LARGEFILE);
+      if(src_fd == -1)
+        return -1;
+
+      dst_fullpath = src_fullpath_;
+
+      dst_fd = fs::mktemp(dst_fullpath,O_WRONLY|O_LARGEFILE);
+      if(dst_fd == -1)
+        return cleanup_on_error(src_fd);
+
+      rv = fs::clonefile(src_fd,dst_fd);
+      if(rv == -1)
+        return cleanup_on_error(src_fd,dst_fd,dst_fullpath);
+
+      rv = fs::rename(dst_fullpath,src_fullpath_);
+      if(rv == -1)
+        return cleanup_on_error(src_fd,dst_fd,dst_fullpath);
+
+      fs::close(src_fd);
+      fs::close(dst_fd);
+
+      return 0;
+    }
+  }
+}

src/fs_cow.hpp

@@ -0,0 +1,33 @@
+/*
+  ISC License
+
+  Copyright (c) 2018, 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 <sys/stat.h>
+#include <sys/types.h>
+
+namespace fs
+{
+  namespace cow
+  {
+    bool is_eligible(const int flags_, const struct stat &st_);
+    bool is_eligible(const char *fullpath_, const int flags_);
+
+    int  break_link(const char *fullpath_);
+  }
+}

src/fs_mktemp.cpp

@@ -0,0 +1,71 @@
+/*
+  ISC License
+
+  Copyright (c) 2018, 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.
+*/
+
+#include "fs_base_open.hpp"
+
+#include <fcntl.h>
+#include <string.h>
+
+#include <cstdlib>
+
+using std::string;
+
+static
+string
+generate_tmp_path(const string &base_)
+{
+  string tmp;
+
+  tmp = base_;
+  tmp += '_';
+  for(int i = 0; i < 6; i++)
+    tmp += ('A' + (std::rand() % 26));
+
+  return tmp;
+}
+
+namespace fs
+{
+  int
+  mktemp(string    &base_,
+         const int  flags_)
+  {
+    int fd;
+    int count;
+    int flags;
+    string tmppath;
+
+    fd    = -1;
+    count = 10;
+    flags = (flags_ | O_EXCL | O_CREAT);
+    while(count-- > 0)
+      {
+        tmppath = generate_tmp_path(base_);
+
+        fd = fs::open(tmppath,flags,S_IWUSR);
+        if((fd == -1) && (errno == EEXIST))
+          continue;
+        else if(fd != -1)
+          base_ = tmppath;
+
+        return fd;
+      }
+
+    return (errno=EEXIST,-1);
+  }
+}

src/fs_mktemp.hpp

@@ -0,0 +1,28 @@
+/*
+  ISC License
+
+  Copyright (c) 2018, 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 <string>
+
+namespace fs
+{
+  int
+  mktemp(std::string &base_,
+         const int    flags_);
+}

src/getxattr.cpp

@@ -210,6 +210,8 @@ _getxattr_controlfile(const Config &config,
         _getxattr_controlfile_bool(config.ignorepponrename,attrvalue);
       else if(attr[2] == "security_capability")
         _getxattr_controlfile_bool(config.security_capability,attrvalue);
+      else if(attr[2] == "link_cow")
+        _getxattr_controlfile_bool(config.link_cow,attrvalue);
       else if(attr[2] == "policies")
         _getxattr_controlfile_policies(config,attrvalue);
       else if(attr[2] == "version")

src/listxattr.cpp

@@ -1,5 +1,5 @@
 /*
-  Copyright (c) 2016, Antonio SJ Musumeci <trapexit@spawn.link>
+  Copyright (c) 2018, 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
@@ -52,6 +52,7 @@ _listxattr_controlfile(char         *list,
     ("user.mergerfs.nullrw")
     ("user.mergerfs.ignorepponrename")
     ("user.mergerfs.security_capability")
+    ("user.mergerfs.link_cow")
     ("user.mergerfs.policies")
     ("user.mergerfs.version")
     ("user.mergerfs.pid");

src/open.cpp

@@ -16,61 +16,67 @@
 
 #include <fuse.h>
 
-#include <fcntl.h>
-
-#include <string>
-#include <vector>
-
 #include "config.hpp"
 #include "errno.hpp"
 #include "fileinfo.hpp"
 #include "fs_base_open.hpp"
+#include "fs_cow.hpp"
 #include "fs_path.hpp"
 #include "rwlock.hpp"
 #include "ugid.hpp"
 
+#include <fcntl.h>
+
+#include <string>
+#include <vector>
+
 using std::string;
 using std::vector;
 using mergerfs::Policy;
 
 static
 int
-_open_core(const string *basepath,
-           const char   *fusepath,
-           const int     flags,
-           uint64_t     &fh)
+_open_core(const string *basepath_,
+           const char   *fusepath_,
+           const int     flags_,
+           const bool    link_cow_,
+           uint64_t     &fh_)
 {
   int fd;
   string fullpath;
 
-  fs::path::make(basepath,fusepath,fullpath);
+  fs::path::make(basepath_,fusepath_,fullpath);
+
+  if(link_cow_ && fs::cow::is_eligible(fullpath.c_str(),flags_))
+    fs::cow::break_link(fullpath.c_str());
 
-  fd = fs::open(fullpath,flags);
+  fd = fs::open(fullpath,flags_);
   if(fd == -1)
     return -errno;
 
-  fh = reinterpret_cast<uint64_t>(new FileInfo(fd,fusepath));
+  fh_ = reinterpret_cast<uint64_t>(new FileInfo(fd,fusepath_));
 
   return 0;
 }
 
 static
 int
-_open(Policy::Func::Search  searchFunc,
-      const vector<string> &srcmounts,
-      const uint64_t        minfreespace,
-      const char           *fusepath,
-      const int             flags,
-      uint64_t             &fh)
+_open(Policy::Func::Search  searchFunc_,
+      const vector<string> &srcmounts_,
+      const uint64_t        minfreespace_,
+      const char           *fusepath_,
+      const int             flags_,
+      const bool            link_cow_,
+      uint64_t             &fh_)
 {
   int rv;
   vector<const string*> basepaths;
 
-  rv = searchFunc(srcmounts,fusepath,minfreespace,basepaths);
+  rv = searchFunc_(srcmounts_,fusepath_,minfreespace_,basepaths);
   if(rv == -1)
     return -errno;
 
-  return _open_core(basepaths[0],fusepath,flags,fh);
+  return _open_core(basepaths[0],fusepath_,flags_,link_cow_,fh_);
 }
 
 namespace mergerfs
@@ -78,8 +84,8 @@ namespace mergerfs
   namespace fuse
   {
     int
-    open(const char     *fusepath,
-         fuse_file_info *ffi)
+    open(const char     *fusepath_,
+         fuse_file_info *ffi_)
     {
       const fuse_context      *fc     = fuse_get_context();
       const Config            &config = Config::get(fc);
@@ -89,9 +95,10 @@ namespace mergerfs
       return _open(config.open,
                    config.srcmounts,
                    config.minfreespace,
-                   fusepath,
-                   ffi->flags,
-                   ffi->fh);
+                   fusepath_,
+                   ffi_->flags,
+                   config.link_cow,
+                   ffi_->fh);
     }
   }
 }

src/option_parser.cpp

@@ -197,6 +197,8 @@ parse_and_process_kv_arg(Config            &config,
         rv = parse_and_process(value,config.ignorepponrename);
       else if(key == "security_capability")
         rv = parse_and_process(value,config.security_capability);
+      else if(key == "link_cow")
+        rv = parse_and_process(value,config.link_cow);
     }
 
   if(rv == -1)
@@ -299,12 +301,15 @@ usage(void)
     "                           timeout in seconds before will turn to symlinks.\n"
     "                           default = 3600\n"
     "    -o nullrw=<bool>       Disables reads and writes. For benchmarking.\n"
+    "                           default = false\n"
     "    -o ignorepponrename=<bool>\n"
     "                           Ignore path preserving when performing renames\n"
     "                           and links. default = false\n"
     "    -o security_capability=<bool>\n"
     "                           When disabled return ENOATTR when the xattr\n"
     "                           security.capability is queried. default = true\n"
+    "    -o link_cow=<bool>     delink/clone file on open to simulate CoW.\n"
+    "                           default = false\n"
             << std::endl;
 }
 

src/setxattr.cpp

@@ -1,5 +1,5 @@
 /*
-  Copyright (c) 2016, Antonio SJ Musumeci <trapexit@spawn.link>
+  Copyright (c) 2018, 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
@@ -302,6 +302,10 @@ _setxattr_controlfile(Config       &config,
         return _setxattr_bool(attrval,
                               flags,
                               config.security_capability);
+      else if(attr[2] == "link_cow")
+        return _setxattr_bool(attrval,
+                              flags,
+                              config.link_cow);
       break;
 
     case 4: