From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6BEEC31F985 for ; Tue, 4 Aug 2026 06:00:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785823205; cv=none; b=c3a8b0Pz2yHgn0wJrUzNmC3CibLQbuCg4l0LAzTgirXol4I08Z+szn1Pf028y3L4kKv5Y0fPor+YhG3c1g/xawiH6/8gfAsXz3nkvaYnGki6n4Se4z4vJF/jQuIRo955bGhMfFF6ruxijySkeJ866jHgfFyeoSM+wBLZdAWf6mU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785823205; c=relaxed/simple; bh=Twon7XJBMGVUOGdo2nZilrIP6BG3kW8RZ89KZYTAw2k=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=KBtmj51WEtGJ6Pxg0yR9FgOhPckYcVb7dbkP/YeYdWytvS2QcgulUqjhkNGj1G2+BTFrf+80N+XvUUVmursRV9Q5RmU0HcEjNj5TC8HIMGoQlN1q3p+WOYT0/SUZbD4GCNHFqHzr2jyBgVi5pT6J1RlYOjs/UV24kq8MFE3baf4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=SWoUqxGa; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="SWoUqxGa" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1785823202; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=nqj8Qxuj4PaU5i4QdVpLQG/TB7fOUrL15E/tCKEo5Vg=; b=SWoUqxGai8euIzCfHnTYY2yRex+s6NU5WrLWoosalwgzNyA4JCAg5k6bsLMTghsFlxgn/j DrG9SXdenahlchIRxqZDoDrbYpDsWHRDQpk6Es2yTDbv0gP07LpUcrimhqGvYtZRnBoUaJ T9gq+cJ2Rv+NCrs5e810cxJ9gED9jqo= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-6-TI00wMDjNoeskEpNxjjDjQ-1; Tue, 04 Aug 2026 01:59:59 -0400 X-MC-Unique: TI00wMDjNoeskEpNxjjDjQ-1 X-Mimecast-MFC-AGG-ID: TI00wMDjNoeskEpNxjjDjQ_1785823198 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B784419560AF; Tue, 4 Aug 2026 05:59:57 +0000 (UTC) Received: from oxygen.redhat.com (unknown [10.44.48.84]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id EA5521956087; Tue, 4 Aug 2026 05:59:55 +0000 (UTC) From: Giuseppe Scrivano To: linux-erofs@lists.ozlabs.org Cc: xiang@kernel.org, linux-fsdevel@vger.kernel.org, gscrivan@redhat.com Subject: [PATCH v6] erofs: accept source file descriptor via fsconfig Date: Tue, 4 Aug 2026 07:58:42 +0200 Message-ID: <20260804055949.2927896-1-gscrivan@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Allow userspace to pass an already-opened file descriptor as the mount source instead of a path string. This is useful for tools that already hold an fd to the image, such as composefs reusing an existing erofs backing file. Signed-off-by: Giuseppe Scrivano Reviewed-by: Gao Xiang Acked-by: Christian Brauner (Amutable) Acked-by: Jan Kara --- v5: https://lore.kernel.org/linux-fsdevel/20260728160619.853924-1-gscrivan@redhat.com/ v4: https://lore.kernel.org/linux-fsdevel/20260717134147.1602735-1-gscrivan@redhat.com/ v3: https://lore.kernel.org/linux-fsdevel/20260714154917.489993-1-gscrivan@redhat.com/ v2: https://lore.kernel.org/linux-fsdevel/20260711071137.4130824-1-gscrivan@redhat.com/ v1: https://lore.kernel.org/linux-fsdevel/ak5GfvVfWLJU1EwK@debian/ Documentation/filesystems/erofs.rst | 17 +++++++ fs/erofs/super.c | 73 ++++++++++++++++++++++++----- 2 files changed, 79 insertions(+), 11 deletions(-) diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst index 4230884fb359..d301d9ac946a 100644 --- a/Documentation/filesystems/erofs.rst +++ b/Documentation/filesystems/erofs.rst @@ -137,8 +137,25 @@ fsoffset=%llu Specify block-aligned filesystem offset for the primary d inode_share Enable inode page sharing for this filesystem. Inodes with identical content within the same domain ID can share the page cache. +source=%s (For file-backed mounts) Specify the backing image as a path + or as an already-opened file descriptor. =================== ========================================================= +File-backed mounts +================== + +When CONFIG_EROFS_FS_BACKED_BY_FILE is enabled, EROFS file-backed images +can be mounted directly without a loopback block device. The backing file +can be given either as a path, or as an already-opened file descriptor. + +When a file descriptor is used, the kernel resolves its path and records it +so that /proc/mounts and similar interfaces can still report the mount +source. + +Only regular files are accepted as backing files; to mount an image that +resides on a block device, use the traditional block device mount path +instead. + Sysfs Entries ============= diff --git a/fs/erofs/super.c b/fs/erofs/super.c index 03d108a7a3e5..d40961248a49 100644 --- a/fs/erofs/super.c +++ b/fs/erofs/super.c @@ -386,6 +386,7 @@ static void erofs_default_options(struct erofs_sb_info *sbi) enum { Opt_user_xattr, Opt_acl, Opt_cache_strategy, Opt_dax, Opt_dax_enum, Opt_device, Opt_domain_id, Opt_directio, Opt_fsoffset, Opt_inode_share, + Opt_source, }; static const struct constant_table erofs_param_cache_strategy[] = { @@ -402,17 +403,18 @@ static const struct constant_table erofs_dax_param_enums[] = { }; static const struct fs_parameter_spec erofs_fs_parameters[] = { - fsparam_flag_no("user_xattr", Opt_user_xattr), - fsparam_flag_no("acl", Opt_acl), - fsparam_enum("cache_strategy", Opt_cache_strategy, + fsparam_flag_no("user_xattr", Opt_user_xattr), + fsparam_flag_no("acl", Opt_acl), + fsparam_enum("cache_strategy", Opt_cache_strategy, erofs_param_cache_strategy), - fsparam_flag("dax", Opt_dax), - fsparam_enum("dax", Opt_dax_enum, erofs_dax_param_enums), - fsparam_string("device", Opt_device), - fsparam_string("domain_id", Opt_domain_id), - fsparam_flag_no("directio", Opt_directio), - fsparam_u64("fsoffset", Opt_fsoffset), - fsparam_flag("inode_share", Opt_inode_share), + fsparam_flag("dax", Opt_dax), + fsparam_enum("dax", Opt_dax_enum, erofs_dax_param_enums), + fsparam_string("device", Opt_device), + fsparam_string("domain_id", Opt_domain_id), + fsparam_flag_no("directio", Opt_directio), + fsparam_u64("fsoffset", Opt_fsoffset), + fsparam_flag("inode_share", Opt_inode_share), + fsparam_file_or_string("source", Opt_source), {} }; @@ -437,6 +439,40 @@ static bool erofs_fc_set_dax_mode(struct fs_context *fc, unsigned int mode) return false; } +static int erofs_fc_parse_source(struct fs_context *fc, + struct fs_parameter *param) +{ + struct erofs_sb_info *sbi = fc->s_fs_info; + + if (fc->source || sbi->dif0.file) + return invalf(fc, "Multiple sources"); + + switch (param->type) { + case fs_value_is_string: + fc->source = param->string; + param->string = NULL; + return 0; + case fs_value_is_file: { + char *buf __free(kfree) = kmalloc(PATH_MAX, GFP_KERNEL); + char *p; + + if (!buf) + return -ENOMEM; + p = file_path(param->file, buf, PATH_MAX); + if (IS_ERR(p)) + return PTR_ERR(p); + fc->source = kstrdup(p, GFP_KERNEL); + if (!fc->source) + return -ENOMEM; + sbi->dif0.file = no_free_ptr(param->file); + return 0; + } + default: + WARN_ON_ONCE(true); + return -EINVAL; + } +} + static int erofs_fc_parse_param(struct fs_context *fc, struct fs_parameter *param) { @@ -524,6 +560,8 @@ static int erofs_fc_parse_param(struct fs_context *fc, else set_opt(&sbi->opt, INODE_SHARE); break; + case Opt_source: + return erofs_fc_parse_source(fc, param); } return 0; } @@ -752,13 +790,26 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc) static int erofs_fc_get_tree(struct fs_context *fc) { + struct erofs_sb_info *sbi = fc->s_fs_info; int ret; + if (sbi->dif0.file) { + if (!IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE)) { + errorfc(fc, "source fd option not supported"); + return -EINVAL; + } + if (!S_ISREG(file_inode(sbi->dif0.file)->i_mode) || + !sbi->dif0.file->f_mapping->a_ops->read_folio) { + errorfc(fc, "source is unsupported"); + return -EINVAL; + } + return get_tree_nodev(fc, erofs_fc_fill_super); + } + ret = get_tree_bdev_flags(fc, erofs_fc_fill_super, IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ? GET_TREE_BDEV_QUIET_LOOKUP : 0); if (IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) && ret == -ENOTBLK) { - struct erofs_sb_info *sbi = fc->s_fs_info; struct file *file; if (!fc->source) -- 2.55.0