Create functions can set branches RO on EROFS

README.md

@@ -747,6 +747,12 @@ If all branches are filtered an error will be returned. Typically
 device) depending on the most recent reason for filtering a
 branch. **ENOENT** will be returned if no eligible branch is found.
 
+If **create**, **mkdir**, **mknod**, or **symlink** fail with `EROFS`
+or other fundimental errors then mergerfs will mark any branch found
+to be read-only as such (IE will set the mode `RO`) and will rerun the
+policy and try again. This is mostly for `ext4` filesystems that can
+suddenly become read-only when it encounters an error.
+
 
 #### Path Preservation
 

man/mergerfs.1

@@ -311,12 +311,12 @@ reading FUSE messages which are dispatched to process threads.
 -1 means disabled otherwise acts like \f[C]read-thread-count\f[R].
 (default: -1)
 .IP \[bu] 2
-\f[B]process-thread-queue-depth=INT\f[R]: Sets the number of requests
+\f[B]process-thread-queue-depth=UINT\f[R]: Sets the number of requests
 any single process thread can have queued up at one time.
 Meaning the total memory usage of the queues is queue depth multiplied
 by the number of process threads plus read thread count.
--1 sets the depth to the same as the process thread count.
-(default: -1)
+0 sets the depth to the same as the process thread count.
+(default: 0)
 .IP \[bu] 2
 \f[B]pin-threads=STR\f[R]: Selects a strategy to pin threads to CPUs
 (default: unset)
@@ -937,6 +937,13 @@ Typically \f[B]EROFS\f[R] (read-only filesystem) or \f[B]ENOSPC\f[R] (no
 space left on device) depending on the most recent reason for filtering
 a branch.
 \f[B]ENOENT\f[R] will be returned if no eligible branch is found.
+.PP
+If \f[B]create\f[R], \f[B]mkdir\f[R], \f[B]mknod\f[R], or
+\f[B]symlink\f[R] fail with \f[C]EROFS\f[R] or other fundimental errors
+then mergerfs will mark any branch found to be read-only as such (IE
+will set the mode \f[C]RO\f[R]) and will rerun the policy and try again.
+This is mostly for \f[C]ext4\f[R] filesystems that can suddenly become
+read-only when it encounters an error.
 .SS Path Preservation
 .PP
 Policies, as described below, are of two basic classifications.

src/branches.cpp

@@ -21,10 +21,12 @@
 #include "errno.hpp"
 #include "from_string.hpp"
 #include "fs_glob.hpp"
+#include "fs_is_rofs.hpp"
 #include "fs_realpathize.hpp"
 #include "nonstd/optional.hpp"
 #include "num.hpp"
 #include "str.hpp"
+#include "syslog.hpp"
 
 #include <string>
 
@@ -415,6 +417,24 @@ Branches::to_string(void) const
   return _impl->to_string();
 }
 
+void
+Branches::find_and_set_mode_ro()
+{
+  for(auto &branch : *_impl)
+    {
+      if(branch.mode != Branch::Mode::RW)
+        continue;
+
+      if(!fs::is_rofs_but_not_mounted_ro(branch.path))
+        continue;
+
+      syslog_warning("Branch %s found to be readonly - setting its mode to RO",
+                     branch.path.c_str());
+
+      branch.mode = Branch::Mode::RO;
+    }
+}
+
 SrcMounts::SrcMounts(Branches &b_)
   : _branches(b_)
 {

src/branches.hpp

@@ -76,6 +76,9 @@ public:
   operator CPtr()   const { std::lock_guard<std::mutex> lg(_mutex); return _impl; }
   CPtr operator->() const { std::lock_guard<std::mutex> lg(_mutex); return _impl; }
 
+public:
+  void find_and_set_mode_ro();
+
 private:
   mutable std::mutex _mutex;
   Ptr                _impl;

src/fs_cow.cpp

@@ -22,6 +22,7 @@
 #include "fs_lstat.hpp"
 #include "fs_mktemp.hpp"
 #include "fs_open.hpp"
+#include "fs_path.hpp"
 #include "fs_rename.hpp"
 #include "fs_unlink.hpp"
 
@@ -109,16 +110,14 @@ namespace fs
       int rv;
       int src_fd;
       int dst_fd;
-      string dst_fullpath;
+      std::string dst_fullpath;
 
       src_fd = fs::open(src_fullpath_,O_RDONLY|O_NOFOLLOW);
       if(src_fd == -1)
         return -1;
 
-      dst_fullpath = src_fullpath_;
-
-      dst_fd = fs::mktemp(&dst_fullpath,O_WRONLY);
-      if(dst_fd == -1)
+      std::tie(dst_fd,dst_fullpath) = fs::mktemp(src_fullpath_,O_WRONLY);
+      if(dst_fd < 0)
         return l::cleanup_on_error(src_fd);
 
       rv = fs::clonefile(src_fd,dst_fd);

src/fs_is_rofs.hpp

@@ -0,0 +1,75 @@
+/*
+  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_mktemp.hpp"
+#include "fs_statvfs.hpp"
+#include "fs_unlink.hpp"
+#include "statvfs_util.hpp"
+#include "ugid.hpp"
+
+#include <string>
+
+
+namespace fs
+{
+  static
+  inline
+  bool
+  is_mounted_rofs(const std::string path_)
+  {
+    int rv;
+    struct statvfs st;
+
+    rv = fs::statvfs(path_,&st);
+
+    return ((rv == 0) ? StatVFS::readonly(st) : false);
+  }
+
+  static
+  inline
+  bool
+  is_rofs(std::string path_)
+  {
+    ugid::SetRootGuard const ugid;
+
+    int fd;
+    std::string tmp_filepath;
+
+    std::tie(fd,tmp_filepath) = fs::mktemp_in_dir(path_,O_WRONLY);
+    if(fd < 0)
+      return (fd == -EROFS);
+
+    fs::close(fd);
+    fs::unlink(tmp_filepath);
+
+    return false;
+  }
+
+  static
+  inline
+  bool
+  is_rofs_but_not_mounted_ro(const std::string path_)
+  {
+    if(fs::is_mounted_rofs(path_))
+      return false;
+
+    return fs::is_rofs(path_);
+  }
+}

src/fs_mktemp.cpp

@@ -18,61 +18,74 @@
 
 #include "errno.hpp"
 #include "fs_open.hpp"
-
-#include <cstdlib>
-#include <string>
+#include "fs_path.hpp"
 
 #include <limits.h>
 
-using std::string;
+#include <cstdlib>
+#include <string>
 
-#define PADLEN 6
-#define MAX_ATTEMPTS 10
+#define PAD_LEN             16
+#define MAX_ATTEMPTS        3
 
+static char const CHARS[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 
-static
-string
-generate_tmp_path(const string &base_)
+namespace l
 {
-  string tmp;
+  static
+  std::string
+  generate_tmp_path(std::string const base_)
+  {
+    fs::Path path;
+    std::string filename;
 
-  tmp = base_;
-  if((tmp.size() + PADLEN + 1) > PATH_MAX)
-    tmp.resize(tmp.size() - PADLEN - 1);
-  tmp += '.';
-  for(int i = 0; i < PADLEN; i++)
-    tmp += ('A' + (std::rand() % 26));
+    filename  = '.';
+    for(int i = 0; i < PAD_LEN; i++)
+      filename += CHARS[std::rand() % (sizeof(CHARS) - 1)];
 
-  return tmp;
+    path = base_;
+    path /= filename;
+
+    return path.string();
+  }
 }
 
 namespace fs
 {
-  int
-  mktemp(string    *base_,
-         const int  flags_)
+  std::tuple<int,std::string>
+  mktemp_in_dir(std::string const dirpath_,
+                int const         flags_)
   {
     int fd;
     int count;
     int flags;
-    string tmppath;
+    std::string tmp_filepath;
 
     fd    = -1;
     count = MAX_ATTEMPTS;
     flags = (flags_ | O_EXCL | O_CREAT | O_TRUNC);
     while(count-- > 0)
       {
-        tmppath = generate_tmp_path(*base_);
+        tmp_filepath = l::generate_tmp_path(dirpath_);
 
-        fd = fs::open(tmppath,flags,S_IWUSR);
+        fd = fs::open(tmp_filepath,flags,S_IWUSR);
         if((fd == -1) && (errno == EEXIST))
           continue;
-        else if(fd != -1)
-          *base_ = tmppath;
+        if(fd == -1)
+          return {-errno,std::string{}};
 
-        return fd;
+        return {fd,tmp_filepath};
       }
 
-    return (errno=EEXIST,-1);
+    return {-EEXIST,std::string{}};
+  }
+
+  std::tuple<int,std::string>
+  mktemp(std::string const filepath_,
+         int const         flags_)
+  {
+    ghc::filesystem::path filepath{filepath_};
+
+    return fs::mktemp_in_dir(filepath.parent_path(),flags_);
   }
 }

src/fs_mktemp.hpp

@@ -19,11 +19,15 @@
 #pragma once
 
 #include <string>
-
+#include <tuple>
 
 namespace fs
 {
-  int
-  mktemp(std::string *base,
-         const int    flags);
+  std::tuple<int,std::string>
+  mktemp(std::string const filepath,
+         int const         flags);
+
+  std::tuple<int,std::string>
+  mktemp_in_dir(std::string const dirpath,
+                int const         flags);
 }

src/fs_movefile.cpp

@@ -117,9 +117,8 @@ namespace l
 
     dstfd_filepath = dstfd_branch[0];
     fs::path::append(dstfd_filepath,fusepath_);
-    dstfd_tmp_filepath = dstfd_filepath;
-    dstfd = fs::mktemp(&dstfd_tmp_filepath,O_WRONLY);
-    if(dstfd == -1)
+    std::tie(dstfd,dstfd_tmp_filepath) = fs::mktemp(dstfd_filepath,O_WRONLY);
+    if(dstfd < 0)
       {
         fs::close(srcfd);
         return -ENOSPC;

src/fuse_create.cpp

@@ -207,6 +207,17 @@ namespace FUSE
                    ffi_,
                    mode_,
                    fc->umask);
+    if(rv == -EROFS)
+      {
+        Config::Write()->branches.find_and_set_mode_ro();
+        rv = l::create(cfg->func.getattr.policy,
+                       cfg->func.create.policy,
+                       cfg->branches,
+                       fusepath_,
+                       ffi_,
+                       mode_,
+                       fc->umask);
+      }
 
     return rv;
   }

src/fuse_link.cpp

@@ -352,7 +352,7 @@ namespace FUSE
 
     rv = l::link(cfg,oldpath_,newpath_,st_,timeouts_);
     if(rv == -EXDEV)
-      return l::link_exdev(cfg,oldpath_,newpath_,st_,timeouts_);
+      rv = l::link_exdev(cfg,oldpath_,newpath_,st_,timeouts_);
 
     return rv;
   }

src/fuse_mkdir.cpp

@@ -150,15 +150,28 @@ namespace FUSE
   mkdir(const char *fusepath_,
         mode_t      mode_)
   {
+    int rv;
     Config::Read cfg;
     const fuse_context *fc = fuse_get_context();
     const ugid::Set     ugid(fc->uid,fc->gid);
 
-    return l::mkdir(cfg->func.getattr.policy,
-                    cfg->func.mkdir.policy,
-                    cfg->branches,
-                    fusepath_,
-                    mode_,
-                    fc->umask);
+    rv = l::mkdir(cfg->func.getattr.policy,
+                  cfg->func.mkdir.policy,
+                  cfg->branches,
+                  fusepath_,
+                  mode_,
+                  fc->umask);
+    if(rv == -EROFS)
+      {
+        Config::Write()->branches.find_and_set_mode_ro();
+        rv = l::mkdir(cfg->func.getattr.policy,
+                      cfg->func.mkdir.policy,
+                      cfg->branches,
+                      fusepath_,
+                      mode_,
+                      fc->umask);
+      }
+
+    return rv;
   }
 }

src/fuse_mknod.cpp

@@ -152,16 +152,30 @@ namespace FUSE
         mode_t      mode_,
         dev_t       rdev_)
   {
+    int rv;
     Config::Read cfg;
     const fuse_context *fc = fuse_get_context();
     const ugid::Set     ugid(fc->uid,fc->gid);
 
-    return l::mknod(cfg->func.getattr.policy,
-                    cfg->func.mknod.policy,
-                    cfg->branches,
-                    fusepath_,
-                    mode_,
-                    fc->umask,
-                    rdev_);
+    rv = l::mknod(cfg->func.getattr.policy,
+                  cfg->func.mknod.policy,
+                  cfg->branches,
+                  fusepath_,
+                  mode_,
+                  fc->umask,
+                  rdev_);
+    if(rv == -EROFS)
+      {
+        Config::Write()->branches.find_and_set_mode_ro();
+        rv = l::mknod(cfg->func.getattr.policy,
+                      cfg->func.mknod.policy,
+                      cfg->branches,
+                      fusepath_,
+                      mode_,
+                      fc->umask,
+                      rdev_);
+      }
+
+    return rv;
   }
 }

src/fuse_symlink.cpp

@@ -157,6 +157,16 @@ namespace FUSE
                     target_,
                     linkpath_,
                     st_);
+    if(rv == -EROFS)
+      {
+        Config::Write()->branches.find_and_set_mode_ro();
+        rv = l::symlink(cfg->func.getattr.policy,
+                        cfg->func.symlink.policy,
+                        cfg->branches,
+                        target_,
+                        linkpath_,
+                        st_);
+      }
 
     if(timeouts_ != NULL)
       {