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[Qemu-devel] [PATCH v2 09/10] file-posix: Prepare permission code for fd
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH v2 09/10] file-posix: Prepare permission code for fd switching |
Date: |
Mon, 11 Mar 2019 17:50:16 +0100 |
In order to be able to dynamically reopen the file read-only or
read-write, depending on the users that are attached, we need to be able
to switch to a different file descriptor during the permission change.
This interacts with reopen, which also creates a new file descriptor and
performs permission changes internally. In this case, the permission
change code must reuse the reopen file descriptor instead of creating a
third one.
In turn, reopen can drop its code to copy file locks to the new file
descriptor because that is now done when applying the new permissions.
Signed-off-by: Kevin Wolf <address@hidden>
---
block/file-posix.c | 96 ++++++++++++++++++++++++++++++++++++++++------
1 file changed, 85 insertions(+), 11 deletions(-)
diff --git a/block/file-posix.c b/block/file-posix.c
index 932cc8e58c..e41e0779c6 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -144,6 +144,7 @@ typedef struct BDRVRawState {
uint64_t locked_perm;
uint64_t locked_shared_perm;
+ int perm_change_fd;
BDRVReopenState *reopen_state;
#ifdef CONFIG_XFS
@@ -845,7 +846,8 @@ static int raw_handle_perm_lock(BlockDriverState *bs,
}
static int raw_reconfigure_getfd(BlockDriverState *bs, int flags,
- int *open_flags, Error **errp)
+ int *open_flags, bool force_dup,
+ Error **errp)
{
BDRVRawState *s = bs->opaque;
int fd = -1;
@@ -871,6 +873,11 @@ static int raw_reconfigure_getfd(BlockDriverState *bs, int
flags,
assert((s->open_flags & O_ASYNC) == 0);
#endif
+ if (!force_dup && *open_flags == s->open_flags) {
+ /* We're lucky, the existing fd is fine */
+ return s->fd;
+ }
+
if ((*open_flags & ~fcntl_flags) == (s->open_flags & ~fcntl_flags)) {
/* dup the original fd */
fd = qemu_dup(s->fd);
@@ -935,7 +942,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
qemu_opts_to_qdict(opts, state->options);
rs->fd = raw_reconfigure_getfd(state->bs, state->flags, &rs->open_flags,
- &local_err);
+ true, &local_err);
if (local_err) {
error_propagate(errp, local_err);
ret = -1;
@@ -951,14 +958,6 @@ static int raw_reopen_prepare(BDRVReopenState *state,
ret = -EINVAL;
goto out_fd;
}
-
- /* Copy locks to the new fd */
- ret = raw_apply_lock_bytes(NULL, rs->fd, s->locked_perm,
- s->locked_shared_perm, false, errp);
- if (ret < 0) {
- ret = -EINVAL;
- goto out_fd;
- }
}
s->reopen_state = state;
@@ -2696,12 +2695,78 @@ static QemuOptsList raw_create_opts = {
static int raw_check_perm(BlockDriverState *bs, uint64_t perm, uint64_t shared,
Error **errp)
{
- return raw_handle_perm_lock(bs, RAW_PL_PREPARE, perm, shared, errp);
+ BDRVRawState *s = bs->opaque;
+ BDRVRawReopenState *rs = NULL;
+ int open_flags;
+ int ret;
+
+ if (s->perm_change_fd) {
+ /*
+ * In the context of reopen, this function may be called several times
+ * (directly and recursively while change permissions of the parent).
+ * This is even true for children that don't inherit from the original
+ * reopen node, so s->reopen_state is not set.
+ *
+ * Ignore all but the first call.
+ */
+ return 0;
+ }
+
+ if (s->reopen_state) {
+ /* We already have a new file descriptor to set permissions for */
+ assert(s->reopen_state->perm == perm);
+ assert(s->reopen_state->shared_perm == shared);
+ rs = s->reopen_state->opaque;
+ s->perm_change_fd = rs->fd;
+ } else {
+ /* We may need a new fd if auto-read-only switches the mode */
+ ret = raw_reconfigure_getfd(bs, bs->open_flags, &open_flags,
+ false, errp);
+ if (ret < 0) {
+ return ret;
+ } else if (ret != s->fd) {
+ s->perm_change_fd = ret;
+ }
+ }
+
+ /* Prepare permissions on old fd to avoid conflicts between old and new,
+ * but keep everything locked that new will need. */
+ ret = raw_handle_perm_lock(bs, RAW_PL_PREPARE, perm, shared, errp);
+ if (ret < 0) {
+ goto fail;
+ }
+
+ /* Copy locks to the new fd */
+ if (s->perm_change_fd) {
+ ret = raw_apply_lock_bytes(NULL, s->perm_change_fd, perm, ~shared,
+ false, errp);
+ if (ret < 0) {
+ raw_handle_perm_lock(bs, RAW_PL_ABORT, 0, 0, NULL);
+ goto fail;
+ }
+ }
+ return 0;
+
+fail:
+ if (s->perm_change_fd && !s->reopen_state) {
+ qemu_close(s->perm_change_fd);
+ }
+ s->perm_change_fd = 0;
+ return ret;
}
static void raw_set_perm(BlockDriverState *bs, uint64_t perm, uint64_t shared)
{
BDRVRawState *s = bs->opaque;
+
+ /* For reopen, we have already switched to the new fd (.bdrv_set_perm is
+ * called after .bdrv_reopen_commit) */
+ if (s->perm_change_fd && s->fd != s->perm_change_fd) {
+ qemu_close(s->fd);
+ s->fd = s->perm_change_fd;
+ }
+ s->perm_change_fd = 0;
+
raw_handle_perm_lock(bs, RAW_PL_COMMIT, perm, shared, NULL);
s->perm = perm;
s->shared_perm = shared;
@@ -2709,6 +2774,15 @@ static void raw_set_perm(BlockDriverState *bs, uint64_t
perm, uint64_t shared)
static void raw_abort_perm_update(BlockDriverState *bs)
{
+ BDRVRawState *s = bs->opaque;
+
+ /* For reopen, .bdrv_reopen_abort is called afterwards and will close
+ * the file descriptor. */
+ if (s->perm_change_fd && !s->reopen_state) {
+ qemu_close(s->perm_change_fd);
+ }
+ s->perm_change_fd = 0;
+
raw_handle_perm_lock(bs, RAW_PL_ABORT, 0, 0, NULL);
}
--
2.20.1
[Qemu-devel] [PATCH v2 09/10] file-posix: Prepare permission code for fd switching,
Kevin Wolf <=
[Qemu-devel] [PATCH v2 08/10] file-posix: Lock new fd in raw_reopen_prepare(), Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 07/10] file-posix: Store BDRVRawState.reopen_state during reopen, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 06/10] file-posix: Factor out raw_reconfigure_getfd(), Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 05/10] file-posix: Fix bdrv_open_flags() for snapshot=on, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 04/10] block: Make permission changes in reopen less wrong, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 03/10] block: Avoid useless local_err, Kevin Wolf, 2019/03/11
[Qemu-devel] [PATCH v2 02/10] qemu-iotests: commit to backing file with auto-read-only, Kevin Wolf, 2019/03/11