[Libguestfs] [nbdkit PATCH 1/2] nbd: Move transaction info from heap to stack
Eric Blake
eblake at redhat.com
Mon Jul 1 22:18:11 UTC 2019
Prepare for the next patch using new API from libnbd by first
refactoring the per-transaction information to initialize the
semaphore earlier, and to use stack allocation rather than the heap.
---
plugins/nbd/nbd.c | 119 ++++++++++++++++++++++++----------------------
1 file changed, 61 insertions(+), 58 deletions(-)
diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c
index b9199644..5aeab9e8 100644
--- a/plugins/nbd/nbd.c
+++ b/plugins/nbd/nbd.c
@@ -59,8 +59,10 @@
struct transaction {
int64_t cookie;
sem_t sem;
+ uint32_t early_err;
uint32_t err;
struct transaction *next;
+ struct nbdkit_extents *extents;
};
/* The per-connection handle */
@@ -400,42 +402,36 @@ nbdplug_reader (void *handle)
return NULL;
}
-/* Register a cookie and return a transaction. */
-static struct transaction *
-nbdplug_register (struct handle *h, int64_t cookie)
+/* Prepare for a transaction. */
+static void
+nbdplug_prepare (struct transaction *trans)
+{
+ memset (trans, 0, sizeof *trans);
+ if (sem_init (&trans->sem, 0, 0))
+ assert (false);
+}
+
+/* Register a cookie and kick the I/O thread. */
+static void
+nbdplug_register (struct handle *h, struct transaction *trans, int64_t cookie)
{
- struct transaction *trans;
char c = 0;
if (cookie == -1) {
nbdkit_error ("command failed: %s", nbd_get_error ());
- errno = nbd_get_errno ();
- return NULL;
+ trans->early_err = nbd_get_errno ();
+ return;
}
nbdkit_debug ("cookie %" PRId64 " started by state machine", cookie);
- trans = calloc (1, sizeof *trans);
- if (!trans) {
- nbdkit_error ("unable to track transaction: %m");
- return NULL;
- }
/* While locked, kick the reader thread and add our transaction */
ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&h->trans_lock);
- if (write (h->fds[1], &c, 1) != 1 && errno != EAGAIN) {
- nbdkit_error ("write to pipe: %m");
- free (trans);
- return NULL;
- }
- if (sem_init (&trans->sem, 0, 0)) {
- nbdkit_error ("unable to create semaphore: %m");
- free (trans);
- return NULL;
- }
+ if (write (h->fds[1], &c, 1) != 1 && errno != EAGAIN)
+ nbdkit_debug ("failed to kick reader thread: %m");
trans->cookie = cookie;
trans->next = h->trans;
h->trans = trans;
- return trans;
}
/* Perform the reply half of a transaction. */
@@ -444,22 +440,20 @@ nbdplug_reply (struct handle *h, struct transaction *trans)
{
int err;
- if (!trans) {
- assert (errno);
- return -1;
+ if (trans->early_err)
+ err = trans->early_err;
+ else {
+ while ((err = sem_wait (&trans->sem)) == -1 && errno == EINTR)
+ /* try again */;
+ if (err) {
+ nbdkit_debug ("failed to wait on semaphore: %m");
+ err = EIO;
+ }
+ else
+ err = trans->err;
}
-
- while ((err = sem_wait (&trans->sem)) == -1 && errno == EINTR)
- /* try again */;
- if (err) {
- nbdkit_debug ("failed to wait on semaphore: %m");
- err = EIO;
- }
- else
- err = trans->err;
if (sem_destroy (&trans->sem))
abort ();
- free (trans);
errno = err;
return err ? -1 : 0;
}
@@ -719,11 +713,12 @@ nbdplug_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
uint32_t flags)
{
struct handle *h = handle;
- struct transaction *s;
+ struct transaction s;
assert (!flags);
- s = nbdplug_register (h, nbd_aio_pread (h->nbd, buf, count, offset, 0));
- return nbdplug_reply (h, s);
+ nbdplug_prepare (&s);
+ nbdplug_register (h, &s, nbd_aio_pread (h->nbd, buf, count, offset, 0));
+ return nbdplug_reply (h, &s);
}
/* Write data to the file. */
@@ -732,12 +727,13 @@ nbdplug_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
uint32_t flags)
{
struct handle *h = handle;
- struct transaction *s;
+ struct transaction s;
uint32_t f = flags & NBDKIT_FLAG_FUA ? LIBNBD_CMD_FLAG_FUA : 0;
assert (!(flags & ~NBDKIT_FLAG_FUA));
- s = nbdplug_register (h, nbd_aio_pwrite (h->nbd, buf, count, offset, f));
- return nbdplug_reply (h, s);
+ nbdplug_prepare (&s);
+ nbdplug_register (h, &s, nbd_aio_pwrite (h->nbd, buf, count, offset, f));
+ return nbdplug_reply (h, &s);
}
/* Write zeroes to the file. */
@@ -745,7 +741,7 @@ static int
nbdplug_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
{
struct handle *h = handle;
- struct transaction *s;
+ struct transaction s;
uint32_t f = 0;
assert (!(flags & ~(NBDKIT_FLAG_FUA | NBDKIT_FLAG_MAY_TRIM)));
@@ -754,8 +750,9 @@ nbdplug_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
f |= LIBNBD_CMD_FLAG_NO_HOLE;
if (flags & NBDKIT_FLAG_FUA)
f |= LIBNBD_CMD_FLAG_FUA;
- s = nbdplug_register (h, nbd_aio_zero (h->nbd, count, offset, f));
- return nbdplug_reply (h, s);
+ nbdplug_prepare (&s);
+ nbdplug_register (h, &s, nbd_aio_zero (h->nbd, count, offset, f));
+ return nbdplug_reply (h, &s);
}
/* Trim a portion of the file. */
@@ -763,12 +760,13 @@ static int
nbdplug_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
{
struct handle *h = handle;
- struct transaction *s;
+ struct transaction s;
uint32_t f = flags & NBDKIT_FLAG_FUA ? LIBNBD_CMD_FLAG_FUA : 0;
assert (!(flags & ~NBDKIT_FLAG_FUA));
- s = nbdplug_register (h, nbd_aio_trim (h->nbd, count, offset, f));
- return nbdplug_reply (h, s);
+ nbdplug_prepare (&s);
+ nbdplug_register (h, &s, nbd_aio_trim (h->nbd, count, offset, f));
+ return nbdplug_reply (h, &s);
}
/* Flush the file to disk. */
@@ -776,18 +774,20 @@ static int
nbdplug_flush (void *handle, uint32_t flags)
{
struct handle *h = handle;
- struct transaction *s;
+ struct transaction s;
assert (!flags);
- s = nbdplug_register (h, nbd_aio_flush (h->nbd, 0));
- return nbdplug_reply (h, s);
+ nbdplug_prepare (&s);
+ nbdplug_register (h, &s, nbd_aio_flush (h->nbd, 0));
+ return nbdplug_reply (h, &s);
}
static int
nbdplug_extent (void *opaque, const char *metacontext, uint64_t offset,
uint32_t *entries, size_t nr_entries, int *error)
{
- struct nbdkit_extents *extents = opaque;
+ struct transaction *trans = opaque;
+ struct nbdkit_extents *extents = trans->extents;
assert (strcmp (metacontext, "base:allocation") == 0);
assert (nr_entries % 2 == 0);
@@ -810,13 +810,15 @@ nbdplug_extents (void *handle, uint32_t count, uint64_t offset,
uint32_t flags, struct nbdkit_extents *extents)
{
struct handle *h = handle;
- struct transaction *s;
+ struct transaction s;
uint32_t f = flags & NBDKIT_FLAG_REQ_ONE ? LIBNBD_CMD_FLAG_REQ_ONE : 0;
assert (!(flags & ~NBDKIT_FLAG_REQ_ONE));
- s = nbdplug_register (h, nbd_aio_block_status (h->nbd, count, offset,
- extents, nbdplug_extent, f));
- return nbdplug_reply (h, s);
+ nbdplug_prepare (&s);
+ s.extents = extents;
+ nbdplug_register (h, &s, nbd_aio_block_status (h->nbd, count, offset,
+ &s, nbdplug_extent, f));
+ return nbdplug_reply (h, &s);
}
/* Cache a portion of the file. */
@@ -824,11 +826,12 @@ static int
nbdplug_cache (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
{
struct handle *h = handle;
- struct transaction *s;
+ struct transaction s;
assert (!flags);
- s = nbdplug_register (h, nbd_aio_cache (h->nbd, count, offset, 0));
- return nbdplug_reply (h, s);
+ nbdplug_prepare (&s);
+ nbdplug_register (h, &s, nbd_aio_cache (h->nbd, count, offset, 0));
+ return nbdplug_reply (h, &s);
}
static struct nbdkit_plugin plugin = {
--
2.20.1
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