From patchwork Fri Apr 22 18:02:46 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Schoenebeck X-Patchwork-Id: 12823986 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C3767C433F5 for ; Fri, 22 Apr 2022 18:24:55 +0000 (UTC) Received: from localhost ([::1]:57728 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nhxxe-0001tE-9e for qemu-devel@archiver.kernel.org; Fri, 22 Apr 2022 14:24:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33958) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nhxcR-0000t5-Do for qemu-devel@nongnu.org; Fri, 22 Apr 2022 14:03:01 -0400 Received: from kylie.crudebyte.com ([5.189.157.229]:53115) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nhxcN-0000jd-Ao for qemu-devel@nongnu.org; Fri, 22 Apr 2022 14:02:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=kylie; h=Content-Type:Content-Transfer-Encoding: MIME-Version:Message-ID:Date:Subject:Cc:To:From:References:In-Reply-To: Content-ID:Content-Description; bh=XRgs5dgoBGBDr9oS5MRbFhujpNneuzIzg2K4+SgByuA=; b=LTDQ4JRHSj7PS7jOvG31dv/Q7W ZB5cT+8p9nbf0eUz5yz+8PNMcOu8i0/sHYrLMr3C/t55uXOeknvcQDdlGTXTeMpLgihR40eBAQrJl P8l8Yv+c2+K3v1qKaaDgvgjT/zsxA/Gt8AP0vETbSgpH+/Oypsirx7HCyP9w9S5r9Ny+XmwPHYsPh OD0V3dy2DL0UwsPda7DPkigL/etquLdpVrlB4a09h5JMZbQruEXzTWncpVrqar8Pu+2lSR9If/7vj 6Sfamqo8kSVgsRbeLyTkBYnX6ubInNVSO4lRPybZO0yubOK1HC2gLVQOlrVaDga2fNKMRVP8a1TwZ a5O+Mt7SbmZCZ5whMbAq6J/sbt3uRetJNum0op4p4Znw31xcjBGhLnzh6SjDFFt3BbvYihp6cKqn7 dkTGuC1GoUabk3W6/3J1KoJHonNV04yf5QB93sTVhwRrcZxIdWrKbEz6Z4ct2yZuBSshH8WGtUbiz nHkhgpU2Sp4VB5Nd4X/4W4aZjSWomDcCPXUPtxBntMzd5yZ2VuUorQlLZkeLD+smipJlYjfUoGSJz jOZzjLoKQXDyvGhRGNtsJdM0GXy9JXuSlLg+kwYpj7/s3+tMQV1MB6hBmAYF+UHfpIB3b4kVxThdl Ha2e37FPpqkbh9tzHmQsXrvnrM6fckHGNMhBwlTnM=; From: Christian Schoenebeck To: qemu-devel@nongnu.org Cc: Will Cohen , Greg Kurz , Michael Roitzsch , Keno Fischer , Dominique Martinet , Eric Van Hensbergen , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, v9fs-developer@lists.sourceforge.net, Latchesar Ionkov Subject: [RFC PATCH] 9p: case-insensitive host filesystems Date: Fri, 22 Apr 2022 20:02:46 +0200 Message-ID: <1757498.AyhHxzoH2B@silver> MIME-Version: 1.0 Received-SPF: pass client-ip=5.189.157.229; envelope-from=qemu_oss@crudebyte.com; helo=kylie.crudebyte.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Now that 9p support for macOS hosts just landed in QEMU 7.0 and with support for Windows hosts on the horizon [1], the question is how to deal with case- insensitive host filesystems, which are very common on those two systems? I made some tests, e.g. trying to setup a 9p root fs Linux installation on a macOS host as described in the QEMU HOWTO [2], which at a certain point causes the debootstrap script to fail when trying to unpack the 'libpam-runtime' package. That's because it would try to create this symlink: /usr/share/man/man7/PAM.7.gz -> /usr/share/man/man7/pam.7.gz which fails with EEXIST on a case-insensitive APFS. Unfortunately you can't easily switch an existing APFS partition to case-sensitivity. It requires to reformat the entire partition, loosing all your data, etc. So I did a quick test with QEMU as outlined below, trying to simply let 9p server "eat" EEXIST errors in such cases, but then I realized that most of the time it would not even come that far, as Linux client would first send a 'Twalk' request to check whether target symlink entry already exists, and as it gets a positive response from 9p server (again, due to case-insensitivity) client would stop right there without even trying to send a 'Tsymlink' request. So maybe it's better to handle case-insensitivity entirely on client side? I've read that some generic "case fold" code has landed in the Linux kernel recently that might do the trick? Should 9p server give a hint to 9p client that it's a case-insensitive fs? And if yes, once per entire exported fs or rather for each directory (as there might be submounts on host)? [1] https://lore.kernel.org/all/20220408171013.912436-1-bmeng.cn@gmail.com/ [2] https://wiki.qemu.org/Documentation/9p_root_fs --- hw/9pfs/9p-local.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) } err = fchownat(dirfd, name, credp->fc_uid, credp->fc_gid, @@ -983,6 +1018,25 @@ static int local_link(FsContext *ctx, V9fsPath *oldpath, ret = linkat(odirfd, oname, ndirfd, name, 0); if (ret < 0) { +#if CONFIG_DARWIN + if (errno == EEXIST) { + printf(" -> linkat(odirfd=%d, oname='%s', ndirfd=%d, name='%s') = EEXIST\n", odirfd, oname, ndirfd, name); + } + if (errno == EEXIST && + strcmp(oname, name) && !p9_stricmp(oname, name)) + { + struct stat st1, st2; + const int cur_errno = errno; + if (!fstatat(odirfd, oname, &st1, AT_SYMLINK_NOFOLLOW) && + !fstatat(ndirfd, name, &st2, AT_SYMLINK_NOFOLLOW) && + st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino) + { + printf(" -> iCASE SAME\n"); + ret = 0; + } + errno = cur_errno; + } +#endif goto out_close; } diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c index d42ce6d8b8..d6cb45c758 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -39,6 +39,10 @@ #endif #endif #include +#ifdef CONFIG_DARWIN +#include +#include +#endif #ifndef XFS_SUPER_MAGIC #define XFS_SUPER_MAGIC 0x58465342 @@ -57,6 +61,18 @@ typedef struct { int mountfd; } LocalData; +#ifdef CONFIG_DARWIN + +/* Compare strings case-insensitive (assuming UTF-8 encoding). */ +static int p9_stricmp(const char *a, const char *b) +{ + g_autofree gchar *cia = g_utf8_casefold(a, -1); + g_autofree gchar *cib = g_utf8_casefold(b, -1); + return g_utf8_collate(cia, cib); +} + +#endif + int local_open_nofollow(FsContext *fs_ctx, const char *path, int flags, mode_t mode) { @@ -931,6 +947,25 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath, fs_ctx->export_flags & V9FS_SM_NONE) { err = symlinkat(oldpath, dirfd, name); if (err) { +#if CONFIG_DARWIN + if (errno == EEXIST) { + printf(" -> symlinkat(oldpath='%s', dirfd=%d, name='%s') = EEXIST\n", oldpath, dirfd, name); + } + if (errno == EEXIST && + strcmp(oldpath, name) && !p9_stricmp(oldpath, name)) + { + struct stat st1, st2; + const int cur_errno = errno; + if (!fstatat(dirfd, oldpath, &st1, AT_SYMLINK_NOFOLLOW) && + !fstatat(dirfd, name, &st2, AT_SYMLINK_NOFOLLOW) && + st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino) + { + printf(" -> iCASE SAME\n"); + err = 0; + } + errno = cur_errno; + } +#endif goto out;