| Message ID | 1757498.AyhHxzoH2B@silver (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC] 9p: case-insensitive host filesystems | expand |
Christian Schoenebeck wrote on Fri, Apr 22, 2022 at 08:02:46PM +0200: > 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? I haven't tried, but settings S_CASEFOLD on every inodes i_flags might do what you want client-side. That's easy enough to test and could be a mount option Even with that it's possible to do a direct open without readdir first if one knows the path and I that would only be case-insensitive if the backing server is case insensitive though, so just setting the option and expecting it to work all the time might be a little bit optimistic... I believe guess that should be an optimization at best. Ideally the server should tell the client they are casefolded somehow, but 9p doesn't have any capability/mount time negotiation besides msize so that's difficult with the current protocol.
On Freitag, 22. April 2022 21:57:40 CEST Dominique Martinet wrote: > Christian Schoenebeck wrote on Fri, Apr 22, 2022 at 08:02:46PM +0200: > > 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? > > I haven't tried, but settings S_CASEFOLD on every inodes i_flags might do > what you want client-side. > That's easy enough to test and could be a mount option I just made a quick test using: diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c index 08f48b70a741..5d8e77daed53 100644 --- a/fs/9p/vfs_inode.c +++ b/fs/9p/vfs_inode.c @@ -257,6 +257,7 @@ int v9fs_init_inode(struct v9fs_session_info *v9ses, inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); inode->i_mapping->a_ops = &v9fs_addr_operations; inode->i_private = NULL; + inode->i_flags |= S_CASEFOLD; switch (mode & S_IFMT) { case S_IFIFO: Unfortunately that did not help much. I still get EEXIST error e.g. when trying 'ln -s foo FOO'. I am not sure though whether there would be more code places to touch or whether that's even the expected behaviour with S_CASEFOLD for some reason. > Even with that it's possible to do a direct open without readdir first > if one knows the path and I that would only be case-insensitive if the > backing server is case insensitive though, so just setting the option > and expecting it to work all the time might be a little bit > optimistic... I believe guess that should be an optimization at best. > > Ideally the server should tell the client they are casefolded somehow, > but 9p doesn't have any capability/mount time negotiation besides msize > so that's difficult with the current protocol.
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;
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; }