This commit adds an example implementation of a custom storage plugin
that uses SSHFS [0] as the underlying filesystem.

The implementation is very similar to that of the NFS plugin; as a
prerequisite, it is currently necessary to use pubkey auth and have
the host's root user's public key deployed to the remote host like so:

  ssh-copy-id -i ~/.ssh/id_my_private_key \
    -o UserKnownHostsFile=/etc/pve/priv/known_hosts [USER]@[HOST]

Then, the storage can be added as follows:

  pvesm add sshfs [STOREID] \
    --username [USER] \
    --server [HOST] \
    --sshfs-remote-path [ABS PATH ON REMOTE] \
    --path /mnt/path/to/storage \
    --sshfs-private-key ~/.ssh/id_my_private_key

If the host is part of a cluster, other nodes may connect to the
remote without any additional setup required. This is because we copy
the private key to `/etc/pve/priv/storage/$KEYNAME.key` and use the
cluster-wide `/etc/pve/priv/known_hosts` file. Also mark each SSHFS
storage as `shared` by default in order to make use of this.

Note: Because there's currently no way to officially and permanently
mark a storage as shared (like some built-in plugins [1]) set
`$scfg->{shared} = 1;` in `on_add_hook`. This has almost the same
effect as modifying `@PVE::Storage::Plugin::SHARED_STORAGE` directly,
except that the `shared` is written to `/etc/pve/storage.cfg`.

[0]: https://github.com/libfuse/sshfs
[1]: 
https://git.proxmox.com/?p=pve-storage.git;a=blob;f=src/PVE/Storage/Plugin.pm;h=4e16420f667f196e8eb99ae7c9f3f1d3e13791fb;hb=refs/heads/master#l37

Signed-off-by: Max Carrara <m.carr...@proxmox.com>
---
Changes rfc-v1 --> v1:
  * rework most of the plugin
  * cease to call methods of DirPlugin (plugins should be isolated;
    we don't want to encourage third-party devs to do that)
  * handle SSH private key as sensitive property and place it on pmxcfs
  * make storage shared
  * manually implement attribute handling ("notes", "protected" for
    backups)

 .../lib/PVE/Storage/Custom/SSHFSPlugin.pm     | 398 ++++++++++++++++++
 1 file changed, 398 insertions(+)
 create mode 100644 example/sshfs-plugin/lib/PVE/Storage/Custom/SSHFSPlugin.pm

diff --git a/example/sshfs-plugin/lib/PVE/Storage/Custom/SSHFSPlugin.pm 
b/example/sshfs-plugin/lib/PVE/Storage/Custom/SSHFSPlugin.pm
new file mode 100644
index 0000000..75b29c1
--- /dev/null
+++ b/example/sshfs-plugin/lib/PVE/Storage/Custom/SSHFSPlugin.pm
@@ -0,0 +1,398 @@
+package PVE::Storage::Custom::SSHFSPlugin;
+
+use strict;
+use warnings;
+
+use feature 'signatures';
+
+use Cwd qw();
+use Encode qw(decode encode);
+use File::Path qw(make_path);
+use File::Basename qw(dirname);
+use IO::File;
+use POSIX;
+
+use PVE::ProcFSTools;
+use PVE::Tools qw(
+    file_copy
+    file_get_contents
+    file_set_contents
+    run_command
+);
+
+use base qw(PVE::Storage::Plugin);
+
+my $CLUSTER_KNOWN_HOSTS = "/etc/pve/priv/known_hosts";
+
+# Plugin Definition
+
+sub api {
+    return 11;
+}
+
+sub type {
+    return 'sshfs';
+}
+
+sub plugindata {
+    return {
+       content => [
+           {
+               images => 1,
+               rootdir => 1,
+               vztmpl => 1,
+               iso => 1,
+               backup => 1,
+               snippets => 1,
+               none => 1,
+           },
+           {
+               images => 1,
+               rootdir => 1,
+           },
+       ],
+       format => [
+           {
+               raw => 1,
+               qcow2 => 1,
+               vmdk => 1,
+           },
+           'qcow2',
+       ],
+       'sensitive-properties' => {
+           'sshfs-private-key' => 1,
+       },
+    };
+}
+
+sub properties {
+    return {
+       'sshfs-remote-path' => {
+           description => "Path on the remote filesystem used for SSHFS. Must 
be absolute.",
+           type => 'string',
+           format => 'pve-storage-path',
+       },
+       'sshfs-private-key' => {
+           description => "Path to the private key to use for SSHFS.",
+           type => 'string',
+           format => 'pve-storage-path',
+       }
+    };
+}
+
+sub options {
+    return {
+       disable => { optional => 1 },
+       path => { fixed => 1 },
+       'create-base-path' => { optional => 1 },
+       content => { optional => 1 },
+       'create-subdirs' => { optional => 1 },
+       'content-dirs' => { optional => 1 },
+       'prune-backups' => { optional => 1 },
+       'max-protected-backups' => { optional => 1 },
+       format => { optional => 1 },
+       bwlimit => { optional => 1 },
+       preallocation => { optional => 1 },
+       nodes => { optional => 1 },
+       shared => { optional => 1 },
+
+       # SSHFS Options
+       username => {},
+       server => {},
+       'sshfs-remote-path' => {},
+       port => { optional => 1 },
+       'sshfs-private-key' => { optional => 1 },
+   };
+}
+
+# SSHFS Helpers
+
+my sub sshfs_remote_from_config: prototype($) ($scfg) {
+    my ($user, $host, $remote_path) = $scfg->@{qw(username server 
sshfs-remote-path)};
+    return "${user}\@${host}:${remote_path}";
+}
+
+my sub sshfs_private_key_path: prototype($) ($storeid) {
+    return "/etc/pve/priv/storage/$storeid.key";
+}
+
+my sub sshfs_common_ssh_opts: prototype($) ($storeid) {
+    my $private_key_path = sshfs_private_key_path($storeid);
+
+    my @common_opts = (
+       '-o', "UserKnownHostsFile=${CLUSTER_KNOWN_HOSTS}",
+       '-o', 'GlobalKnownHostsFile=none',
+       '-o', "IdentityFile=${private_key_path}",
+    );
+
+    return @common_opts;
+}
+
+my sub sshfs_set_private_key: prototype($$) ($storeid, $src_key_path) {
+    die "path of private key file not specified" if !defined($src_key_path);
+    die "path of private key file does not exist" if ! -e $src_key_path;
+    die "path of private key file does not point to a file" if ! -f 
$src_key_path;
+
+    my $dest_key_path = sshfs_private_key_path($storeid);
+
+    my $dest_key_parent_dir = dirname($dest_key_path);
+    if (! -e $dest_key_parent_dir) {
+       make_path($dest_key_parent_dir, { chmod => 0700 });
+    } else {
+       die "'$dest_key_path' already exists" if -e $dest_key_path;
+    }
+
+    file_copy($src_key_path, $dest_key_path, undef, 600);
+
+    return undef;
+}
+
+my sub sshfs_remove_private_key: prototype($) ($storeid) {
+    my $key_path = sshfs_private_key_path($storeid);
+    unlink($key_path) or $! == ENOENT or die "failed to remove private key 
'$key_path' - $!\n";
+
+    return undef;
+}
+
+my sub sshfs_is_mounted: prototype($) ($scfg) {
+    my $remote = sshfs_remote_from_config($scfg);
+
+    my $mountpoint = Cwd::realpath($scfg->{path}); # Resolve symlinks
+    return 0 if !defined($mountpoint);
+
+    my $mountdata = PVE::ProcFSTools::parse_proc_mounts();
+
+    my $has_found_mountpoint = grep {
+       $_->[0] =~ m|^\Q${remote}\E$|
+       && $_->[1] eq $mountpoint
+       && $_->[2] eq 'fuse.sshfs'
+    } $mountdata->@*;
+
+    return $has_found_mountpoint != 0;
+}
+
+my sub sshfs_mount: prototype($$) ($scfg, $storeid) {
+    my $remote = sshfs_remote_from_config($scfg);
+    my ($port, $mountpoint) = $scfg->@{qw(port path)};
+
+    my @common_opts = sshfs_common_ssh_opts($storeid);
+    my $cmd = [
+       '/usr/bin/sshfs', @common_opts,
+       '-o', 'noatime',
+    ];
+
+    push($cmd->@*, '-p', $port) if $port;
+    push($cmd->@*, $remote, $mountpoint);
+
+    eval {
+       run_command(
+           $cmd,
+           timeout => 10,
+           errfunc => sub { warn "$_[0]\n"; },
+       );
+    };
+    if (my $err = $@) {
+       die "failed to mount SSHFS storage '$remote' at '$mountpoint': $@\n";
+    }
+
+    die "SSHFS storage '$remote' not mounted at '$mountpoint' despite reported 
success\n"
+       if ! sshfs_is_mounted($scfg);
+
+    return;
+}
+
+my sub sshfs_umount: prototype($) ($scfg) {
+    my $mountpoint = $scfg->{path};
+
+    my $cmd = ['/usr/bin/umount', $mountpoint];
+
+    eval {
+       run_command(
+           $cmd,
+           timeout => 10,
+           errfunc => sub { warn "$_[0]\n"; },
+       );
+    };
+    if (my $err = $@) {
+       die "failed to unmount SSHFS at '$mountpoint': $err\n";
+    }
+
+    return;
+}
+
+# Storage Implementation
+
+sub on_add_hook ($class, $storeid, $scfg, %sensitive) {
+    $scfg->{shared} = 1; # mark SSHFS storages as shared by default
+
+    eval {
+       my $src_key_path = $sensitive{'sshfs-private-key'};
+       sshfs_set_private_key($storeid, $src_key_path);
+    };
+    die "error while adding SSHFS storage '${storeid}': $@\n" if $@;
+
+    return undef;
+}
+
+sub on_update_hook ($class, $storeid, $scfg, %sensitive) {
+    return undef if !exists($sensitive{'sshfs-private-key'});
+
+    my $src_key_path = $sensitive{'sshfs-private-key'};
+
+    if (!defined($src_key_path)) {
+       warn "removing private key for SSHFS storage '${storeid}'";
+       warn "the storage might not be mountable without a private key!";
+
+       eval { sshfs_remove_private_key($storeid); };
+       die $@ if $@;
+
+       return undef;
+    }
+
+    my $dest_key_path = sshfs_private_key_path($storeid);
+    my $dest_key_path_tmp = "${dest_key_path}.old";
+
+    file_copy($dest_key_path, $dest_key_path_tmp) if -e $dest_key_path;
+
+    eval { file_copy($src_key_path, $dest_key_path, undef, 600); };
+
+    if (my $err = $@) {
+       if (-e $dest_key_path_tmp) {
+           warn "attempting to restore previous private key for storage 
'${storeid}'\n";
+           eval { file_copy($dest_key_path_tmp, $dest_key_path, undef, 600); };
+           warn "$@\n" if $@;
+
+           unlink $dest_key_path_tmp;
+       }
+
+       die "failed to set private key for SSHFS storage '${storeid}': $err\n";
+    }
+
+    unlink $dest_key_path_tmp;
+
+    return undef;
+}
+
+sub on_delete_hook ($class, $storeid, $scfg) {
+    eval { sshfs_remove_private_key($storeid); };
+    warn $@ if $@;
+
+    eval { sshfs_umount($scfg) if sshfs_is_mounted($scfg); };
+    warn $@ if $@;
+
+    return undef;
+}
+
+sub check_connection ($class, $storeid, $scfg) {
+    my ($user, $host, $port) = $scfg->@{qw(username server port)};
+
+    my @common_opts = sshfs_common_ssh_opts($storeid);
+    my $cmd = [
+       '/usr/bin/ssh',
+       '-T',
+       @common_opts,
+       '-o', 'BatchMode=yes',
+       '-o', 'ConnectTimeout=5',
+    ];
+
+    push($cmd->@*, "-p", $port) if $port;
+    push($cmd->@*, "${user}\@${host}", 'exit 0');
+
+    eval {
+       run_command(
+           $cmd,
+           timeout => 10,
+           errfunc => sub { warn "$_[0]\n"; },
+       );
+    };
+    if (my $err = $@) {
+       warn "$err";
+       return 0;
+    }
+
+    return 1;
+}
+
+sub activate_storage ($class, $storeid, $scfg, $cache) {
+    my $mountpoint = $scfg->{path};
+
+    if (!sshfs_is_mounted($scfg)) {
+       if ($scfg->{'create-base-path'} // 1) {
+           make_path($mountpoint);
+       }
+
+       die "unable to activate storage '$storeid' - directory '$mountpoint' 
does not exist\n"
+           if ! -d $mountpoint;
+
+       sshfs_mount($scfg, $storeid);
+    }
+
+    $class->SUPER::activate_storage($storeid, $scfg, $cache);
+    return;
+}
+
+sub get_volume_attribute ($class, $scfg, $storeid, $volname, $attribute) {
+    my ($vtype) = $class->parse_volname($volname);
+    return if $vtype ne 'backup';
+
+    my $volume_path = PVE::Storage::Plugin->filesystem_path($scfg, $volname);
+
+    if ($attribute eq 'notes') {
+       my $notes_path = $volume_path . $class->SUPER::NOTES_EXT;
+
+       if (-f $notes_path) {
+           my $notes = file_get_contents($notes_path);
+           return eval { decode('UTF-8', $notes, 1) } // $notes;
+       }
+
+       return "";
+    }
+
+    if ($attribute eq 'protected') {
+       return -e PVE::Storage::protection_file_path($volume_path) ? 1 : 0;
+    }
+
+    return;
+}
+
+sub update_volume_attribute ($class, $scfg, $storeid, $volname, $attribute, 
$value) {
+    my ($vtype, $name) = $class->parse_volname($volname);
+    die "only backups support attribute '$attribute'\n" if $vtype ne 'backup';
+
+    my $volume_path = PVE::Storage::Plugin->filesystem_path($scfg, $volname);
+
+    if ($attribute eq 'notes') {
+       my $notes_path = $volume_path . $class->SUPER::NOTES_EXT;
+
+       if (defined($value)) {
+           my $encoded_notes = encode('UTF-8', $value);
+           file_set_contents($notes_path, $encoded_notes);
+       } else {
+           unlink $notes_path or $! == ENOENT or die "could not delete notes - 
$!\n";
+       }
+
+       return;
+    }
+
+    if ($attribute eq 'protected') {
+       my $protection_path = PVE::Storage::protection_file_path($volume_path);
+
+       # Protection already set or unset
+       return if !((-e $protection_path) xor $value);
+
+       if ($value) {
+           my $fh = IO::File->new($protection_path, O_CREAT, 0644)
+               or die "unable to create protection file '$protection_path' - 
$!\n";
+           close($fh);
+       } else {
+           unlink $protection_path or $! == ENOENT
+               or die "could not delete protection file '$protection_path' - 
$!\n";
+       }
+
+       return;
+    }
+
+    die "attribute '$attribute' is not supported for storage type 
'$scfg->{type}'\n";
+}
+
+1;
-- 
2.39.5



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