similar to: [PATCH] Fix typos in plugin manual

[still a work in progress, as I finish rebasing to capture the ideas raised on the list, but posting now for initial feedback] The NBD protocol supports Forced Unit Access (FUA) as a more efficient way to wait for just one write to land in persistent storage, rather than all outstanding writes at the time of a flush; modeled after the kernel's block I/O flag of the same name. While we can

The callback doesn't make much sense: Could the value change per-connection? Unlikely. This is a property of the plugin as a whole. I changed the name to "errno_is_preserved", because it's not about the reliability of errno, but about whether errno is preserved across calls. --- docs/nbdkit-plugin.pod | 37 +++++++++------------------------

Hi, We've been using a modified nbdkit (ours is cbdkit internally) for about half a year now and since you guys appear to be working on a next version of the API I wanted to go over some of the limitations we hit with nbdkit that we think others may also hit for consideration into the batch of changes you are making to the api. About Us: Our primary use for nbdkit is to facilitate a disk

The NBD protocol supports Forced Unit Access (FUA) as a more efficient way to wait for just one write to land in persistent storage, rather than all outstanding writes at the time of a flush; modeled after the kernel's block I/O flag of the same name. While we can emulate the proper semantics with a full-blown flush, there are some plugins that can properly pass the FUA flag on to the end

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

Originally, I thought that since the plugin always emulates .zero with a fallback to .pwrite, we didn't need to expose the backend's .can_zero to plugins. But there is another consideration, as shown at least in the nbd plugin: a plugin may implement a .zero callback that depends on support from a remote endpoint. If the remote endpoint doesn't support zeroes, then the plugin HAS to

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

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

This lets you write simple plugins in Tcl. All the basic features of nbdkit are supported, but serious Tcl users will probably want to enhance the plugin further. Unfortunately Tcl as a language is not very well suited to handling binary data. It prefers to store binary data in UCS-2 strings, meaning that every second byte is wasted. Also there appears to be no way to replace part of such a

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 |

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 +-

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 +-

Here's my second attempt at a filter API. As before, .config and .config_complete can only call the next->.config or next->.config_complete methods in the chain respectively. The change is with the connected functions (get_size, pread, pwrite, etc.). Here we pass a struct of next functions allowing the filter to call any functions on the plugin, so for example a write can turn into

It is very unlikely that the value of errno after completing the glue code in between the completion of the user's callback and the point in time where we construct the client's reply is going to be untouched, which means that we are likely to send the wrong error code across the wire. Add a new callback which determines whether we can trust errno; defaulting to true for C plugins, where

In commit c306fa93ab and neighbors (v1.15.1), a concerted effort went into caching the results of .can_FOO callbacks, with commit messages demonstrating that a plugin with a slow callback should not have that delay magnified multiple times. But nothing was added to the testsuite at the time, and with the sh and eval plugins, we still have two scenarios where we did not take advantage of the

--- plugins/python/nbdkit-python-plugin.pod | 22 +++++++++++-- plugins/python/python.c | 41 +++++++++++++++++++++++++ 2 files changed, 61 insertions(+), 2 deletions(-) diff --git a/plugins/python/nbdkit-python-plugin.pod b/plugins/python/nbdkit-python-plugin.pod index 0fd4dcb..2bc4722 100644 --- a/plugins/python/nbdkit-python-plugin.pod +++

The retry filter was originally written to be the closest filter to the plugin, with no other filters in between; as such, the reopen command did not have to worry about recursion or about .prepare or .finalize. But it is not that much harder to properly track everything needed to allow other filters to be retried, as long as we are careful to never call .finalize unless .prepare succeeded, never

We want some testsuite coverage of handling non-1 .can_flush values. The only in-tree plugin with this property is nbd-standalone, but it doesn't get frequently tested, not to mention that the next patch will change it to work with older nbdkit. Signed-off-by: Eric Blake <eblake@redhat.com> --- work in progress: currently compiles but fails during test; posting it now to show my

Hi. Whenever I notice a typo someplace, I fix it in a local "typo tree". Attached is 2 patches from that tree, one against OpenBSD and the other against Portable. Is it worth fixing these? -Daz. -- Darren Tucker (dtucker at zip.com.au) GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69 Good judgement comes with experience. Unfortunately, the experience

On 01/16/2018 08:40 AM, Richard W.M. Jones wrote: > Here's my second attempt at a filter API. > > As before, .config and .config_complete can only call the > next->.config or next->.config_complete methods in the chain > respectively. > > The change is with the connected functions (get_size, pread, pwrite, > etc.). Here we pass a struct of next functions