Messages in this thread Patch in this message | | | From | Christian Schoenebeck <> | Subject | [RFC PATCH] 9p: case-insensitive host filesystems | Date | Fri, 22 Apr 2022 20:02:46 +0200 |
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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(+)
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 <sys/ioctl.h> +#ifdef CONFIG_DARWIN +#include <glib.h> +#include <glib/gprintf.h> +#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; } 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; } -- 2.32.0 (Apple Git-132)
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