Spawn "mount" on branches when waiting for mounts enabled

DEPENDENCIES

@@ -7,9 +7,9 @@
 * fmt: https://github.com/fmtlib/fmt
 * concurrentqueue: https://github.com/cameron314/concurrentqueue
 * scope_guard: https://github.com/Neargye/scope_guard
+* subprocess: https://github.com/arun11299/cpp-subprocess
 * boost
   * download boost
   * ./bootstrap.sh
   * ./b2 tools/bcp
-  * ./dist/bin/bcp pool/pool.hpp <target_dir>
   * ./dist/bin/bcp unordered/concurrent_flat_map.hpp <target_dir>

mkdocs/docs/config/branches_mount_timeout.md → mkdocs/docs/config/branches-mount-timeout.md

@@ -1,6 +1,7 @@
 # branches-mount-timeout
 
-Default: `0`
+* type: `UINT` (seconds)
+* default: `0`
 
 mergerfs is compatible with any path, whether it be a mount point or a
 directory on your [root
@@ -17,8 +18,10 @@ offers a way to enforce mount dependencies using the
 option in /etc/fstab, applying this to every branch path is both
 cumbersome and susceptible to errors.
 
-`branches-mount-timeout` will cause mergerfs to wait for all branches
-to become "mounted." The logic to determine "mounted" is as follows.
+`branches-mount-timeout` will cause mergerfs to first attempt to mount
+each branch if the branch appears to be on the same filesystem as the
+`mergerfs` mount point and then wait for all branches to become
+"mounted." The logic to determine "mounted" is as follows.
 
 1. It is mounted if the branch directory has the extended attribute
    `user.mergerfs.branch`
@@ -28,13 +31,25 @@ to become "mounted." The logic to determine "mounted" is as follows.
    attribute `user.mergerfs.branch_mounts_here`
 4. It is **not** mounted if the branch directory contains
    a file named `.mergerfs.branch_mounts_here`
-5. It is mounted if the `st_dev` value of the mergerfs mountpoint is
+5. It is mounted if the `st_dev` value of the mergerfs mount point is
    different from the branch path.
 
+These files and xattrs are used to help `mergerfs` know whether or not
+a directory happens to be a branch or is the underlying directory
+mount point.
+
+
 **NOTE:** If on a `systemd` based system and using `fstab` it is a
 good idea to set the mount option
 [x-systemd.mount-timeout](https://www.freedesktop.org/software/systemd/man/latest/systemd.mount.html#x-systemd.mount-timeout=)
-to some value longer than `branches-mount-timeout`.
+to some value longer than `branches-mount-timeout` otherwise `systemd`
+might kill `mergerfs` before it finishes waiting.
+
+**NOTE:** The way `mergerfs` attempts to mount the branch is by
+calling out to the system command `mount` with the branch as the
+target. If that path is configured in `/etc/fstab` as a mount point
+then `mount` should attempt to mount it with the settings defined in
+`fstab`.
 
 
 ## branches-mount-timeout-fail

mkdocs/docs/config/branches.md

@@ -66,8 +66,8 @@ A convenient way to configure branches is to use
 
 ## branch setup
 
-mergerfs does not require any special setup of branch paths in order
-to be used however here are some suggestions.
+`mergerfs` does **not** require any special setup of branch paths in
+order to be used however here are some suggestions.
 
 
 ### layout
@@ -132,12 +132,13 @@ $ sudo chattr +i /mnt/hdd/10T-XYZ
 ```
 
 The extended attribute `user.mergerfs.branch_mounts_here` is used by
-the [branches-mount-timeout](branches_mount_timeout.md) option to
+the [branches-mount-timeout](branches-mount-timeout.md) option to
 recognize whether or not a mergerfs branch path points to the intended
 filesystem.
 
 The `chattr` is likely to only work on EXT{2,3,4} filesystems but will
-restrict even `root` from modifying the directory or its content.
+restrict even `root` from modifying the directory or its content but
+is still able to be a mount point.
 
 
 #### mounted filesystems

mkdocs/docs/config/options.md

@@ -33,6 +33,12 @@ config file.
   key=val / ini style format.
 * **[branches](branches.md)**: Colon delimited list of branches. Used
   primarily in config file.
+* **[branches-mount-timeout](branches-mount-timeout.md)=UINT**: Number
+  of seconds to wait at startup for branches to be a mount other than
+  the mountpoint's filesystem. (default: 0)
+* **[branches-mount-timeout-fail](branches-mount-timeout.md##branches-mount-timeout-fail)=BOOL**:
+  If set to `true` then if `branches-mount-timeout` expires it will
+  exit rather than continuing. (default: false)
 * **[minfreespace](minfreespace.md)=SIZE**: The minimum available
   space of a branch necessary to be considered for a create
   [policy](functions_categories_policies.md). This is a default value
@@ -102,9 +108,6 @@ config file.
 * **nfsopenhack=off|git|all**: A workaround for exporting mergerfs
   over NFS where there are issues with creating files for write while
   setting the mode to read-only. (default: off)
-* **branches-mount-timeout=UINT**: Number of seconds to wait at
-  startup for branches to be a mount other than the mountpoint's
-  filesystem. (default: 0)
 * **[follow-symlinks](follow-symlinks.md)=never|directory|regular|all**:
   Turns symlinks into what they point to. (default: never)
 * **[link-exdev](link-exdev.md)=passthrough|rel-symlink|abs-base-symlink|abs-pool-symlink**:

mkdocs/docs/faq/why_isnt_it_working.md

@@ -36,36 +36,27 @@ and [FAQ](configuration_and_policies.md) for policy recommendations.
 
 ## Why do I get an "out of space" / "no space left on device" / ENOSPC error even though there appears to be lots of space available?
 
-First make sure you've read the sections about [policies, path
-preservation, branch
-filtering,](../config/functions_categories_policies.md) and the
-options [minfreespace](../config/minfreespace.md),
-[moveonenospc](../config/moveonenospc.md),
-[statfs](../config/statfs.md), and
-[statfs_ignore](../config/statfs.md#statfs_ignore).
-
-mergerfs is simply presenting a union of the content within multiple
+One or multiple of the below are likely causing branches
+
+* [minfreespace](../config/minfreespace.md) could be filtering out
+  branches
+* if using an `ep*`
+  [policy](../config/functions_categories_policies.md) there may not
+  be an available branch
+* due to [branch modes](../config/branches.md#branch-mode) being set
+  to to `NC` or `RO` branches will be excluded from consideration
+* if using `ext4` ensure you are not running into reserve limits (use
+  `tune2fs -m 0` to remove the reserve)
+* it is possible that the filesystem selected by the policy has run
+  out of inodes (check with `df -i`)
+
+mergerfs is presenting a union of the content within multiple
 branches. The reported free space is an aggregate of space available
-within the pool (behavior modified by `statfs` and
-`statfs_ignore`). It does not represent a contiguous space. In the
-same way that read-only filesystems, those with quotas, or reserved
-space report the full theoretical space available. Not the practical
-usable space.
-
-Due to using an `existing path` based policy, setting a [branch's
-mode](../config/branches.md#branch-mode) to `NC` or `RO`, a
-filesystems read-only status, and/or `minfreespace` setting it is
-[perfectly
-valid](../config/functions_categories_policies.md#filtering) that
-`ENOSPC` / "out of space" / "no space left on device" be returned when
-attempting to create a file despite there being actual space available
-somewhere in the pool. It is doing what was asked of it: filtering
-possible branches due to those settings. If that is not the behavior
-you want you need to modify the settings accordingly.
-
-It is also possible that the filesystem selected has run out of
-inodes. Use `df -i` to list the total and available inodes per
-filesystem.
+within the pool (behavior modified by [statfs](../config/statfs.md)
+and [statfs_ignore](../config/statfs.md#statfs_ignore)). It does not
+represent a contiguous space. In the same way that read-only
+filesystems, those with quotas, or reserved space report the full
+theoretical space available. Not the practical usable space.
 
 
 ## Why isn't the create policy working?
@@ -76,7 +67,7 @@ First, confirm the policy is configured as expected by using the
 [runtime interface](../runtime_interfaces.md).
 
 ```shell
-$ getfattr -n user.mergerfs.category.create /mnt/mergerfs/.mergerfs
+$ sudo getfattr -n user.mergerfs.category.create /mnt/mergerfs/.mergerfs
 # file: mnt/mergerfs/.mergerfs
 user.mergerfs.category.create="mfs"
 ```
@@ -87,8 +78,8 @@ where it was created.
 
 
 ```shell
-$ touch /mnt/mergerfs/new-file
-$ getfattr -n user.mergerfs.allpaths /mnt/mergerfs/new-file
+$ sudo touch /mnt/mergerfs/new-file
+$ sudo getfattr -n user.mergerfs.allpaths /mnt/mergerfs/new-file
 # file: mnt/mergerfs/new-file
 user.mergerfs.allpaths="/mnt/hdd/drive1/new-file"
 ```

mkdocs/mkdocs.yml

@@ -69,7 +69,7 @@ nav:
   - config/options.md
   - config/deprecated_options.md
   - config/branches.md
-  - config/branches_mount_timeout.md
+  - config/branches-mount-timeout.md
   - config/functions_categories_policies.md
   - config/minfreespace.md
   - config/func_readdir.md

src/fs_mount.cpp

@@ -0,0 +1,10 @@
+#include "fs_mount.hpp"
+
+#include "subprocess.hpp"
+
+
+int
+fs::mount(const std::string &tgt_)
+{
+  return subprocess::call({"mount",tgt_});
+}

src/fs_mount.hpp

@@ -0,0 +1,8 @@
+#pragma once
+
+#include <string>
+
+namespace fs
+{
+  int mount(const std::string &tgt);
+}

src/fs_wait_for_mount.cpp

@@ -19,6 +19,7 @@
 #include "fs_wait_for_mount.hpp"
 #include "syslog.hpp"
 
+#include "fs_mount.hpp"
 #include "fs_exists.hpp"
 #include "fs_lgetxattr.hpp"
 #include "fs_lstat.hpp"
@@ -123,13 +124,13 @@ _wait_for_mount(const struct stat               &src_st_,
       for(const auto &path : successes)
         {
           tgt_paths.erase(path);
-          SysLog::info("{} is mounted",path.string());
+          SysLog::info("{} is ready",path.string());
         }
 
       if(first_loop)
         {
           for(const auto &path : failures)
-            SysLog::notice("{} is not mounted, waiting",path.string());
+            SysLog::notice("{} is not ready, waiting",path.string());
           first_loop = false;
         }
 
@@ -138,7 +139,7 @@ _wait_for_mount(const struct stat               &src_st_,
     }
 
   for(auto const &path : failures)
-    SysLog::notice("{} not mounted within timeout",path.string());
+    SysLog::notice("{} not ready within timeout",path.string());
 
   return failures.size();
 }
@@ -157,5 +158,18 @@ fs::wait_for_mount(const fs::Path                  &src_path_,
                   src_path_.string(),
                   strerror(errno));
 
+  for(auto &tgt_path : tgt_paths_)
+    {
+      int rv;
+
+      if(_branch_is_mounted(src_st,tgt_path))
+        continue;
+
+      rv = fs::mount(tgt_path);
+      SysLog::notice("mount {}: {}",
+                     tgt_path.string(),
+                     ((rv == 0) ? "success" : "fail"));
+    }
+
   return ::_wait_for_mount(src_st,tgt_paths_,timeout_);
 }