similar to: [nbdkit PATCH] filters: Make nxdata persistent

Since commit 86fdb48c6a5362d66865493d9d2172166f99722e we have stored the connection object in thread-local storage. In this very large, but mostly mechanical change we stop passing the connection pointer around everywhere, and instead use the value stored in thread-local storage. This assumes a 1-1 mapping between the connection and the current thread which is true in *most* places.

nbdkit_debug implicitly prints the plugin name. However this leads to confusing debug messages such as: nbdkit: pattern[1]: debug: prepare nbdkit: pattern[1]: debug: prepare (in this instance, two different prepare functions were called in different filters, but neither filter name was shown). By printing the filter name in the debug message we improve the output: nbdkit: pattern[1]:

Anywhere that we compute 'f = container_of(b)' then use 'f->backend.', we can instead just use 'b->'. Similarly, during registration, we can use the 'filename' input rather than our just-copied 'f->filename'. Signed-off-by: Eric Blake <eblake@redhat.com> --- server/filters.c | 170 ++++++++++++++++++++++------------------------- 1 file

Filters can be placed in front of plugins to modify their behaviour. This commit adds the <nbdkit-filter.h> header file, the manual page, the ‘filterdir’ directory (like ‘plugindir’), the ‘filters/’ source directory which will contain the actual filters, the ‘--filters’ parameter, and the filters backend logic. --- Makefile.am | 2 +- TODO | 17 +-

This was previously used as ‘nxdata’ and stored a tuple of ’b->next’ and the real filter handle. However after recent changes we don't need it. We can use ‘b->next’ as nxdata, and the handle is passed to us by the calling functions. Inspired by Eric Blakes observations in this email: https://www.redhat.com/archives/libguestfs/2020-February/msg00092.html --- server/filters.c | 217

Filters can be placed in front of plugins to modify their behaviour. This commit adds the <nbdkit-filter.h> header file, the manual page, the ‘filterdir’ directory (like ‘plugindir’), the ‘filters/’ source directory which will contain the actual filters, the ‘--filters’ parameter, and the filters backend logic. --- Makefile.am | 2 +- TODO | 17 +-

Both plugin.c and filter.c add the same three fields on top of struct backend, and use very similar code in initializing them. Let's stop the duplication, by moving those three fields into struct backend, and creating a new backend.c for manipulating them. In turn, we can drop the backend->name() accessor in favor of just directly accessing the name field. This is a net reduction in

The NBD protocol is adding an extension to let servers advertise initialization state to the client: whether the image contains holes, and whether it is known to read as all zeroes. Most filters just pass through the plugin's result (as it is only checked once when first connecting), but we can do useful things in log (mention the setting), extentlist (answer based on the extents we are

This pair of calls allows plugins to describe which extents in the virtual disk are allocated, holes or zeroes. --- docs/nbdkit-filter.pod | 22 +++++++++++ docs/nbdkit-plugin.pod | 86 +++++++++++++++++++++++++++++++++++++++++ include/nbdkit-common.h | 14 ++++++- include/nbdkit-filter.h | 12 +++++- include/nbdkit-plugin.h | 6 ++- server/internal.h | 7 +++- server/filters.c |

This pair of calls allows plugins to describe which extents in the virtual disk are allocated, holes or zeroes. --- docs/nbdkit-filter.pod | 45 +++++++++++++++++ docs/nbdkit-plugin.pod | 106 ++++++++++++++++++++++++++++++++++++++++ include/nbdkit-common.h | 18 ++++++- include/nbdkit-filter.h | 12 ++++- include/nbdkit-plugin.h | 6 ++- server/internal.h | 7 ++- server/extents.c

This pair of calls allows plugins to describe which extents in the virtual disk are allocated, holes or zeroes. --- docs/nbdkit-filter.pod | 64 +++++++++++++++++++++ docs/nbdkit-plugin.pod | 123 ++++++++++++++++++++++++++++++++++++++++ include/nbdkit-common.h | 20 ++++++- include/nbdkit-filter.h | 15 ++++- include/nbdkit-plugin.h | 6 +- server/internal.h | 7 ++-

This pair of calls allows plugins to describe which extents in the virtual disk are allocated, holes or zeroes. --- docs/nbdkit-filter.pod | 89 +++++++++++++++++++ docs/nbdkit-plugin.pod | 96 +++++++++++++++++++++ include/nbdkit-common.h | 10 ++- include/nbdkit-filter.h | 22 ++++- include/nbdkit-plugin.h | 6 +- server/internal.h | 4 + server/extents.c | 186

This pair of calls allows plugins to describe which extents in the virtual disk are allocated, holes or zeroes. --- docs/nbdkit-filter.pod | 92 +++++++++++++++++++++ docs/nbdkit-plugin.pod | 99 +++++++++++++++++++++++ include/nbdkit-common.h | 10 ++- include/nbdkit-filter.h | 22 +++++- include/nbdkit-plugin.h | 6 +- server/internal.h | 4 + server/extents.c | 171

This new pair of callbacks allows plugins to describe which extents in the virtual disk are allocated, holes or zeroes. --- docs/nbdkit-filter.pod | 83 ++++++++++++++++ docs/nbdkit-plugin.pod | 97 +++++++++++++++++++ include/nbdkit-common.h | 10 +- include/nbdkit-filter.h | 22 ++++- include/nbdkit-plugin.h | 6 +- server/internal.h | 4 + server/extents.c | 210

Because we pass a next() pointer to .open, the filter can choose whether to call it first (inner-to-outer completion) or last (outer-to-inner). However, all our filters currently call it first, and this logically lines up with the mirror ordering of outer-to-inner used during .close. Signed-off-by: Eric Blake <eblake@redhat.com> --- docs/nbdkit-filter.pod | 17 +++++++++++++----

On 2/11/20 11:15 AM, Richard W.M. Jones wrote: > Since commit 86fdb48c6a5362d66865493d9d2172166f99722e we have stored > the connection object in thread-local storage. > > In this very large, but mostly mechanical change we stop passing the > connection pointer around everywhere, and instead use the value stored > in thread-local storage. > > This assumes a 1-1 mapping

While our plugin code always advertises WRITE_ZEROES on writable connections (because we can emulate .zero by calling .pwrite), and FUA support when .flush exists (because we can emulate the persistence by calling .flush), it is conceivable that a filter may want to explicitly avoid advertising particular bits. (More to the point, I plan on writing a 'nozero' filter that hides

From: "Richard W.M. Jones" <rjones@redhat.com> This patch may be worth squashing? --- docs/nbdkit-filter.pod | 65 +++++++++++++++++++++++++++++++++++++++++++------ include/nbdkit-filter.h | 29 ++++++++++++---------- src/filters.c | 55 ++++++++++++++++++++--------------------- 3 files changed, 101 insertions(+), 48 deletions(-) diff --git a/docs/nbdkit-filter.pod

Previously, we let a plugin set an error in either thread-local storage (nbdkit_set_error()) or errno, then connections.c would decode which error to use. But with filters in the mix, it is very difficult for a filter to know what error was set by the plugin (particularly since nbdkit_set_error() has no public counterpart for reading the thread-local storage). What's more, if a filter does

>From the protocol document: "NBD_FLAG_CAN_MULTI_CONN: Indicates that the server operates entirely without cache, or that the cache it uses is shared among all connections to the given device. In particular, if this flag is present, then the effects of NBD_CMD_FLUSH and NBD_CMD_FLAG_FUA MUST be visible across all connections when the server sends its reply to that command to