similar to: [nbdkit PATCH] filters: Remove most next_* wrappers

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

I'm about to add an 'exportname' filter, and in the process, I noticed a few shortcomings in our API. Having .default_export makes it easy to answer NBD_INFO_NAME in response to a client request during NBD_OPT_GO, but answering NBD_INFO_DESCRIPTION is awkward - there's no guarantee the export name was given with a description in .list_exports. Note, however, that while we map

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

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

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.

Take advantage of the fact that we can now detect the type of client during --tls=on in order to provide safe dummy content for plaintext clients without having to rewrite plugins to do so. Signed-off-by: Eric Blake <eblake@redhat.com> --- docs/nbdkit-plugin.pod | 4 +- docs/nbdkit-tls.pod | 5 +- filters/tlsdummy/nbdkit-tlsdummy-filter.pod

Similar to the previous patch in caching size, we want to avoid calling into the plugin more than once per connection on any of the flag determination callbacks. The following script demonstrates the speedup, where we avoid repeated calls into a slow can_fua. Pre-patch: $ cat script case "$1" in get_size) echo 1m;; can_fua) sleep 1; echo native;; can_write | can_zero |

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 |

Although it is unusual for a plugin to shrink size on reopen, it is not impossible. Failure to check our bounds could result in violating assumptions in the plugin that all requests are in-bounds. Note that if the plugin gains a larger size, we merely never access the new tail of the file (when the NBD protocol ever gains dynamic resize support, we'll get to revisit how the retry filter fits

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 ++-

When extracting an obvious subset of a larger container (ext2, gzip, partition, tar, xz), it's fairly easy to add a nice updated description for what the client is seeing. Not all clients request the description, but if you are worried about this leaking too much information, it can be silenced with nbdkit-exportname-filter. Signed-off-by: Eric Blake <eblake@redhat.com> --- And maybe

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

On Thu, Oct 03, 2019 at 09:54:37PM -0500, Eric Blake wrote: > Although it is unusual for a plugin to shrink size on reopen, it is > not impossible. Failure to check our bounds could result in violating > assumptions in the plugin that all requests are in-bounds. Note that > if the plugin gains a larger size, we merely never access the new tail > of the file (when the NBD protocol

On Thu, Aug 27, 2020 at 05:03:45PM -0500, Eric Blake wrote: > When extracting an obvious subset of a larger container (ext2, gzip, > partition, tar, xz), it's fairly easy to add a nice updated > description for what the client is seeing. Not all clients request > the description, but if you are worried about this leaking too much > information, it can be silenced with

When we added support for .extents, we had nbdkit unconditionally support structured replies if the client requests them, and the plugin's .can_extents has no impact on what the server advertises. However, while the plugin API doesn't care whether the client requested SR, there is still a case to be made for allowing a filter to prevent SR, at least for testing purposese (such as

This pair of calls allows plugins to describe which extents in the virtual disk are allocated, holes or zeroes. --- docs/nbdkit-filter.pod | 107 ++++++++ docs/nbdkit-plugin.pod | 103 +++++++ include/nbdkit-common.h | 10 +- include/nbdkit-filter.h | 25 +- include/nbdkit-plugin.h | 6 +- server/internal.h | 5 + server/extents.c | 574

>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