285 lines
9.1 KiB
Diff
285 lines
9.1 KiB
Diff
From: Miklos Szeredi <mszeredi@redhat.com>
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Date: Mon, 27 Jan 2020 19:01:17 +0000
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Subject: [PATCH] virtiofsd: passthrough_ll: add fallback for racy ops
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We have two operations that cannot be done race-free on a symlink in
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certain cases: utimes and link.
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Add racy fallback for these if the race-free method doesn't work. We do
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our best to avoid races even in this case:
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- get absolute path by reading /proc/self/fd/NN symlink
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- lookup parent directory: after this we are safe against renames in
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ancestors
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- lookup name in parent directory, and verify that we got to the original
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inode, if not retry the whole thing
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Both utimes(2) and link(2) hold i_lock on the inode across the operation,
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so a racing rename/delete by this fuse instance is not possible, only from
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other entities changing the filesystem.
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If the "norace" option is given, then disable the racy fallbacks.
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Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
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Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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(cherry picked from commit 5fe319a7b19c9c328e6e061bffcf1ff6cc8b89ce)
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---
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tools/virtiofsd/helper.c | 5 +-
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tools/virtiofsd/passthrough_ll.c | 157 +++++++++++++++++++++++++++----
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2 files changed, 145 insertions(+), 17 deletions(-)
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diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
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index b8ec5ac8dc..5531425223 100644
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--- a/tools/virtiofsd/helper.c
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+++ b/tools/virtiofsd/helper.c
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@@ -142,7 +142,10 @@ void fuse_cmdline_help(void)
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" --daemonize run in background\n"
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" -o max_idle_threads the maximum number of idle worker "
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"threads\n"
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- " allowed (default: 10)\n");
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+ " allowed (default: 10)\n"
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+ " -o norace disable racy fallback\n"
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+ " default: false\n"
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+ );
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}
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static int fuse_helper_opt_proc(void *data, const char *arg, int key,
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diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
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index 9815bfa5c5..ac380efcb1 100644
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--- a/tools/virtiofsd/passthrough_ll.c
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+++ b/tools/virtiofsd/passthrough_ll.c
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@@ -98,6 +98,7 @@ enum {
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struct lo_data {
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pthread_mutex_t mutex;
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int debug;
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+ int norace;
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int writeback;
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int flock;
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int xattr;
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@@ -124,10 +125,15 @@ static const struct fuse_opt lo_opts[] = {
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{ "cache=never", offsetof(struct lo_data, cache), CACHE_NEVER },
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{ "cache=auto", offsetof(struct lo_data, cache), CACHE_NORMAL },
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{ "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS },
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-
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+ { "norace", offsetof(struct lo_data, norace), 1 },
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FUSE_OPT_END
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};
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+static void unref_inode(struct lo_data *lo, struct lo_inode *inode, uint64_t n);
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+
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+static struct lo_inode *lo_find(struct lo_data *lo, struct stat *st);
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+
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+
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static struct lo_data *lo_data(fuse_req_t req)
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{
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return (struct lo_data *)fuse_req_userdata(req);
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@@ -347,23 +353,127 @@ static void lo_getattr(fuse_req_t req, fuse_ino_t ino,
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fuse_reply_attr(req, &buf, lo->timeout);
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}
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-static int utimensat_empty_nofollow(struct lo_inode *inode,
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- const struct timespec *tv)
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+static int lo_parent_and_name(struct lo_data *lo, struct lo_inode *inode,
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+ char path[PATH_MAX], struct lo_inode **parent)
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{
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- int res;
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char procname[64];
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+ char *last;
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+ struct stat stat;
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+ struct lo_inode *p;
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+ int retries = 2;
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+ int res;
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+
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+retry:
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+ sprintf(procname, "/proc/self/fd/%i", inode->fd);
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+
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+ res = readlink(procname, path, PATH_MAX);
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+ if (res < 0) {
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+ fuse_log(FUSE_LOG_WARNING, "%s: readlink failed: %m\n", __func__);
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+ goto fail_noretry;
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+ }
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+
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+ if (res >= PATH_MAX) {
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+ fuse_log(FUSE_LOG_WARNING, "%s: readlink overflowed\n", __func__);
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+ goto fail_noretry;
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+ }
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+ path[res] = '\0';
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+
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+ last = strrchr(path, '/');
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+ if (last == NULL) {
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+ /* Shouldn't happen */
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+ fuse_log(
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+ FUSE_LOG_WARNING,
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+ "%s: INTERNAL ERROR: bad path read from proc\n", __func__);
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+ goto fail_noretry;
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+ }
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+ if (last == path) {
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+ p = &lo->root;
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+ pthread_mutex_lock(&lo->mutex);
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+ p->refcount++;
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+ pthread_mutex_unlock(&lo->mutex);
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+ } else {
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+ *last = '\0';
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+ res = fstatat(AT_FDCWD, last == path ? "/" : path, &stat, 0);
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+ if (res == -1) {
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+ if (!retries) {
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+ fuse_log(FUSE_LOG_WARNING,
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+ "%s: failed to stat parent: %m\n", __func__);
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+ }
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+ goto fail;
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+ }
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+ p = lo_find(lo, &stat);
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+ if (p == NULL) {
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+ if (!retries) {
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+ fuse_log(FUSE_LOG_WARNING,
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+ "%s: failed to find parent\n", __func__);
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+ }
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+ goto fail;
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+ }
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+ }
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+ last++;
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+ res = fstatat(p->fd, last, &stat, AT_SYMLINK_NOFOLLOW);
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+ if (res == -1) {
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+ if (!retries) {
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+ fuse_log(FUSE_LOG_WARNING,
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+ "%s: failed to stat last\n", __func__);
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+ }
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+ goto fail_unref;
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+ }
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+ if (stat.st_dev != inode->dev || stat.st_ino != inode->ino) {
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+ if (!retries) {
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+ fuse_log(FUSE_LOG_WARNING,
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+ "%s: failed to match last\n", __func__);
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+ }
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+ goto fail_unref;
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+ }
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+ *parent = p;
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+ memmove(path, last, strlen(last) + 1);
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+
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+ return 0;
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+
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+fail_unref:
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+ unref_inode(lo, p, 1);
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+fail:
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+ if (retries) {
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+ retries--;
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+ goto retry;
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+ }
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+fail_noretry:
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+ errno = EIO;
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+ return -1;
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+}
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+
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+static int utimensat_empty(struct lo_data *lo, struct lo_inode *inode,
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+ const struct timespec *tv)
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+{
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+ int res;
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+ struct lo_inode *parent;
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+ char path[PATH_MAX];
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if (inode->is_symlink) {
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- res = utimensat(inode->fd, "", tv, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
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+ res = utimensat(inode->fd, "", tv, AT_EMPTY_PATH);
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if (res == -1 && errno == EINVAL) {
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/* Sorry, no race free way to set times on symlink. */
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- errno = EPERM;
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+ if (lo->norace) {
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+ errno = EPERM;
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+ } else {
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+ goto fallback;
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+ }
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}
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return res;
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}
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- sprintf(procname, "/proc/self/fd/%i", inode->fd);
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+ sprintf(path, "/proc/self/fd/%i", inode->fd);
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- return utimensat(AT_FDCWD, procname, tv, 0);
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+ return utimensat(AT_FDCWD, path, tv, 0);
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+
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+fallback:
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+ res = lo_parent_and_name(lo, inode, path, &parent);
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+ if (res != -1) {
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+ res = utimensat(parent->fd, path, tv, AT_SYMLINK_NOFOLLOW);
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+ unref_inode(lo, parent, 1);
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+ }
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+
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+ return res;
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}
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static int lo_fi_fd(fuse_req_t req, struct fuse_file_info *fi)
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@@ -387,6 +497,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
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{
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int saverr;
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char procname[64];
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+ struct lo_data *lo = lo_data(req);
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struct lo_inode *inode;
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int ifd;
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int res;
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@@ -459,7 +570,7 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
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if (fi) {
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res = futimens(fd, tv);
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} else {
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- res = utimensat_empty_nofollow(inode, tv);
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+ res = utimensat_empty(lo, inode, tv);
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}
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if (res == -1) {
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goto out_err;
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@@ -709,24 +820,38 @@ static void lo_symlink(fuse_req_t req, const char *link, fuse_ino_t parent,
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lo_mknod_symlink(req, parent, name, S_IFLNK, 0, link);
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}
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-static int linkat_empty_nofollow(struct lo_inode *inode, int dfd,
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- const char *name)
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+static int linkat_empty_nofollow(struct lo_data *lo, struct lo_inode *inode,
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+ int dfd, const char *name)
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{
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int res;
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- char procname[64];
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+ struct lo_inode *parent;
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+ char path[PATH_MAX];
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if (inode->is_symlink) {
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res = linkat(inode->fd, "", dfd, name, AT_EMPTY_PATH);
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if (res == -1 && (errno == ENOENT || errno == EINVAL)) {
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/* Sorry, no race free way to hard-link a symlink. */
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- errno = EPERM;
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+ if (lo->norace) {
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+ errno = EPERM;
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+ } else {
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+ goto fallback;
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+ }
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}
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return res;
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}
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- sprintf(procname, "/proc/self/fd/%i", inode->fd);
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+ sprintf(path, "/proc/self/fd/%i", inode->fd);
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+
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+ return linkat(AT_FDCWD, path, dfd, name, AT_SYMLINK_FOLLOW);
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+
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+fallback:
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+ res = lo_parent_and_name(lo, inode, path, &parent);
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+ if (res != -1) {
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+ res = linkat(parent->fd, path, dfd, name, 0);
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+ unref_inode(lo, parent, 1);
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+ }
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- return linkat(AT_FDCWD, procname, dfd, name, AT_SYMLINK_FOLLOW);
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+ return res;
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}
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static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent,
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@@ -748,7 +873,7 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent,
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e.attr_timeout = lo->timeout;
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e.entry_timeout = lo->timeout;
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- res = linkat_empty_nofollow(inode, lo_fd(req, parent), name);
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+ res = linkat_empty_nofollow(lo, inode, lo_fd(req, parent), name);
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if (res == -1) {
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goto out_err;
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}
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