[Libguestfs] [nbdkit PATCH] filters: Make nxdata persistent

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(a)redhat.com&gt; --- 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