[Libguestfs] [nbdkit PATCH] filters: Make nxdata persistent
Eric Blake
eblake at redhat.com
Tue Feb 11 13:31:11 UTC 2020
Future patches want to allow a filter to pass a single opaque
parameter into another framework (such as ext2fs_open) or even spawn a
helper thread, which requires that nxdata be stable for the entire
life of the connection between .open and .close. Our current approach
of creating a stack-allocated nxdata for every call does not play
nicely with that scheme, so rework things into using a malloc'd
pointer. In fact, if we use struct b_conn as our filter handle, and
merely add an additional field to track the user's handle, then we get
the long-term persistance we desire.
Signed-off-by: Eric Blake <eblake at redhat.com>
---
docs/nbdkit-filter.pod | 7 +-
server/filters.c | 141 ++++++++++++++++++++++++++---------------
2 files changed, 96 insertions(+), 52 deletions(-)
diff --git a/docs/nbdkit-filter.pod b/docs/nbdkit-filter.pod
index 55dfab1..5fed7ca 100644
--- a/docs/nbdkit-filter.pod
+++ b/docs/nbdkit-filter.pod
@@ -131,7 +131,12 @@ C<nbdkit_next_config_complete>, C<nbdkit_next_preconnect>,
C<nbdkit_next_open>) and a structure called C<struct nbdkit_next_ops>.
These abstract the next plugin or filter in the chain. There is also
an opaque pointer C<nxdata> which must be passed along when calling
-these functions.
+these functions. The value of C<nxdata> passed to C<.open> has a
+stable lifetime that lasts to the corresponding C<.close>; with all
+intermediate functions (such ase C<.pread>) receiving the same value
+for convenience; the only exceptions where C<nxdata> is not reused are
+C<.config>, C<.config_complete>, and C<.preconnect>, which are called
+outside the lifetime of a connection.
=head2 Next config, open and close
diff --git a/server/filters.c b/server/filters.c
index ed026f5..2f65818 100644
--- a/server/filters.c
+++ b/server/filters.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2013-2019 Red Hat Inc.
+ * Copyright (C) 2013-2020 Red Hat Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
@@ -49,12 +49,14 @@ struct backend_filter {
struct nbdkit_filter filter;
};
-/* Literally a backend + a connection pointer. This is the
- * implementation of ‘void *nxdata’ in the filter API.
+/* Literally a backend, a connection pointer, and the filter's handle.
+ * This is the implementation of our handle in .open, and serves as
+ * a stable ‘void *nxdata’ in the filter API.
*/
struct b_conn {
struct backend *b;
struct connection *conn;
+ void *handle;
};
/* Note this frees the whole chain. */
@@ -223,26 +225,44 @@ static void *
filter_open (struct backend *b, struct connection *conn, int readonly)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = malloc (sizeof *nxdata);
+
+ if (!nxdata) {
+ nbdkit_error ("malloc: %m");
+ return NULL;
+ }
+
+ nxdata->b = b->next;
+ nxdata->conn = conn;
+ nxdata->handle = NULL;
/* Most filters will call next_open first, resulting in
* inner-to-outer ordering.
*/
if (f->filter.open)
- return f->filter.open (next_open, &nxdata, readonly);
+ nxdata->handle = f->filter.open (next_open, nxdata, readonly);
else if (backend_open (b->next, conn, readonly) == -1)
- return NULL;
+ nxdata->handle = NULL;
else
- return NBDKIT_HANDLE_NOT_NEEDED;
+ nxdata->handle = NBDKIT_HANDLE_NOT_NEEDED;
+ if (nxdata->handle == NULL) {
+ free (nxdata);
+ return NULL;
+ }
+ return nxdata;
}
static void
filter_close (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
+ struct b_conn *nxdata = handle;
- if (handle && f->filter.close)
- f->filter.close (handle);
+ if (handle && f->filter.close) {
+ assert (nxdata->b == b->next && nxdata->conn == conn);
+ f->filter.close (nxdata->handle);
+ free (nxdata);
+ }
}
/* The next_functions structure contains pointers to backend
@@ -421,10 +441,11 @@ filter_prepare (struct backend *b, struct connection *conn, void *handle,
int readonly)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.prepare &&
- f->filter.prepare (&next_ops, &nxdata, handle, readonly) == -1)
+ f->filter.prepare (&next_ops, nxdata, nxdata->handle, readonly) == -1)
return -1;
return 0;
@@ -434,10 +455,11 @@ static int
filter_finalize (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.finalize &&
- f->filter.finalize (&next_ops, &nxdata, handle) == -1)
+ f->filter.finalize (&next_ops, nxdata, nxdata->handle) == -1)
return -1;
return 0;
}
@@ -446,10 +468,11 @@ static int64_t
filter_get_size (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.get_size)
- return f->filter.get_size (&next_ops, &nxdata, handle);
+ return f->filter.get_size (&next_ops, nxdata, nxdata->handle);
else
return backend_get_size (b->next, conn);
}
@@ -458,10 +481,11 @@ static int
filter_can_write (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_write)
- return f->filter.can_write (&next_ops, &nxdata, handle);
+ return f->filter.can_write (&next_ops, nxdata, nxdata->handle);
else
return backend_can_write (b->next, conn);
}
@@ -470,10 +494,11 @@ static int
filter_can_flush (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_flush)
- return f->filter.can_flush (&next_ops, &nxdata, handle);
+ return f->filter.can_flush (&next_ops, nxdata, nxdata->handle);
else
return backend_can_flush (b->next, conn);
}
@@ -482,10 +507,11 @@ static int
filter_is_rotational (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.is_rotational)
- return f->filter.is_rotational (&next_ops, &nxdata, handle);
+ return f->filter.is_rotational (&next_ops, nxdata, nxdata->handle);
else
return backend_is_rotational (b->next, conn);
}
@@ -494,10 +520,11 @@ static int
filter_can_trim (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_trim)
- return f->filter.can_trim (&next_ops, &nxdata, handle);
+ return f->filter.can_trim (&next_ops, nxdata, nxdata->handle);
else
return backend_can_trim (b->next, conn);
}
@@ -506,10 +533,11 @@ static int
filter_can_zero (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_zero)
- return f->filter.can_zero (&next_ops, &nxdata, handle);
+ return f->filter.can_zero (&next_ops, nxdata, nxdata->handle);
else
return backend_can_zero (b->next, conn);
}
@@ -518,10 +546,11 @@ static int
filter_can_fast_zero (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_fast_zero)
- return f->filter.can_fast_zero (&next_ops, &nxdata, handle);
+ return f->filter.can_fast_zero (&next_ops, nxdata, nxdata->handle);
else
return backend_can_fast_zero (b->next, conn);
}
@@ -530,10 +559,11 @@ static int
filter_can_extents (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_extents)
- return f->filter.can_extents (&next_ops, &nxdata, handle);
+ return f->filter.can_extents (&next_ops, nxdata, nxdata->handle);
else
return backend_can_extents (b->next, conn);
}
@@ -542,10 +572,11 @@ static int
filter_can_fua (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_fua)
- return f->filter.can_fua (&next_ops, &nxdata, handle);
+ return f->filter.can_fua (&next_ops, nxdata, nxdata->handle);
else
return backend_can_fua (b->next, conn);
}
@@ -554,10 +585,11 @@ static int
filter_can_multi_conn (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_multi_conn)
- return f->filter.can_multi_conn (&next_ops, &nxdata, handle);
+ return f->filter.can_multi_conn (&next_ops, nxdata, nxdata->handle);
else
return backend_can_multi_conn (b->next, conn);
}
@@ -566,10 +598,11 @@ static int
filter_can_cache (struct backend *b, struct connection *conn, void *handle)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.can_cache)
- return f->filter.can_cache (&next_ops, &nxdata, handle);
+ return f->filter.can_cache (&next_ops, nxdata, nxdata->handle);
else
return backend_can_cache (b->next, conn);
}
@@ -580,10 +613,11 @@ filter_pread (struct backend *b, struct connection *conn, void *handle,
uint32_t flags, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.pread)
- return f->filter.pread (&next_ops, &nxdata, handle,
+ return f->filter.pread (&next_ops, nxdata, nxdata->handle,
buf, count, offset, flags, err);
else
return backend_pread (b->next, conn, buf, count, offset, flags, err);
@@ -595,10 +629,11 @@ filter_pwrite (struct backend *b, struct connection *conn, void *handle,
uint32_t flags, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.pwrite)
- return f->filter.pwrite (&next_ops, &nxdata, handle,
+ return f->filter.pwrite (&next_ops, nxdata, nxdata->handle,
buf, count, offset, flags, err);
else
return backend_pwrite (b->next, conn, buf, count, offset, flags, err);
@@ -609,10 +644,11 @@ filter_flush (struct backend *b, struct connection *conn, void *handle,
uint32_t flags, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.flush)
- return f->filter.flush (&next_ops, &nxdata, handle, flags, err);
+ return f->filter.flush (&next_ops, nxdata, nxdata->handle, flags, err);
else
return backend_flush (b->next, conn, flags, err);
}
@@ -623,11 +659,12 @@ filter_trim (struct backend *b, struct connection *conn, void *handle,
uint32_t flags, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.trim)
- return f->filter.trim (&next_ops, &nxdata, handle, count, offset, flags,
- err);
+ return f->filter.trim (&next_ops, nxdata, nxdata->handle, count, offset,
+ flags, err);
else
return backend_trim (b->next, conn, count, offset, flags, err);
}
@@ -637,10 +674,11 @@ filter_zero (struct backend *b, struct connection *conn, void *handle,
uint32_t count, uint64_t offset, uint32_t flags, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.zero)
- return f->filter.zero (&next_ops, &nxdata, handle,
+ return f->filter.zero (&next_ops, nxdata, nxdata->handle,
count, offset, flags, err);
else
return backend_zero (b->next, conn, count, offset, flags, err);
@@ -652,10 +690,11 @@ filter_extents (struct backend *b, struct connection *conn, void *handle,
struct nbdkit_extents *extents, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.extents)
- return f->filter.extents (&next_ops, &nxdata, handle,
+ return f->filter.extents (&next_ops, nxdata, nxdata->handle,
count, offset, flags,
extents, err);
else
@@ -669,11 +708,11 @@ filter_cache (struct backend *b, struct connection *conn, void *handle,
uint32_t flags, int *err)
{
struct backend_filter *f = container_of (b, struct backend_filter, backend);
- struct b_conn nxdata = { .b = b->next, .conn = conn };
-
+ struct b_conn *nxdata = handle;
+ assert (nxdata->b == b->next && nxdata->conn == conn);
if (f->filter.cache)
- return f->filter.cache (&next_ops, &nxdata, handle,
+ return f->filter.cache (&next_ops, nxdata, nxdata->handle,
count, offset, flags, err);
else
return backend_cache (b->next, conn, count, offset, flags, err);
--
2.24.1
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