[Libguestfs] [PATCH nbdkit 2/2] file: Allow a file descriptor to be passed to the plugin

This allows you to pass in a file descriptor to the plugin, eg: $ exec 6<>/var/tmp/fedora-36.img $ ./nbdkit file fd=6 --run 'nbdinfo $uri' Note this was previously possible on most platforms using /dev/fd/<N>, but not all platforms that have file descriptors support this (although it is POSIX) and it seems better to make this explicit. --- plugins/file/nbdkit-file-plugin.pod | 22 +++++- tests/Makefile.am | 2 + plugins/file/file.c | 108 +++++++++++++++++++--------- tests/test-file-fd.sh | 65 +++++++++++++++++ 4 files changed, 160 insertions(+), 37 deletions(-) diff --git a/plugins/file/nbdkit-file-plugin.pod b/plugins/file/nbdkit-file-plugin.pod index 49c330663..dadbe9432 100644 --- a/plugins/file/nbdkit-file-plugin.pod +++ b/plugins/file/nbdkit-file-plugin.pod @@ -11,6 +11,10 @@ nbdkit-file-plugin - nbdkit file plugin nbdkit file dir=DIRECTORY +=for paragraph + + nbdkit file fd=FILE_DESCRIPTOR + =head1 DESCRIPTION C<nbdkit-file-plugin> is a file serving plugin for L<nbdkit(1)>. @@ -22,10 +26,16 @@ If you use the C<dir> parameter the plugin works in a different mode where it serves files from the given C<DIRECTORY>, chosen by the client using the NBD export name. +If you use the C<fd> parameter then you can pass the file descriptor +of a single disk to the plugin, inherited from the parent process. +This can be useful where special permissions / capabilities are needed +to open the file or you want to run nbdkit in a sandboxed environment. + =head1 PARAMETERS -Either B<file> or B<dir> must be given which controls the mode of the -plugin, either serving a single file or the files in a directory. +B<file>, B<dir> or B<fd> must be given. This controls the mode of the +plugin, either serving a single file, the files in a directory, or a +single file descriptor. =over 4 @@ -72,6 +82,14 @@ read-ahead. See also L<posix_fadvise(2)>. The default is C<normal>. +=item B<fd=>FILE_DESCRIPTOR + +(nbdkit E<ge> 1.34, not Windows) + +The parameter is the number of a file descriptor. Serve the file or +device already open on this file descriptor. The file descriptor is +usually inherited from the parent process. + =item [B<file=>]FILENAME Serve the file named C<FILENAME>. A local block device name can also diff --git a/tests/Makefile.am b/tests/Makefile.am index 3dc428540..3667a1dea 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -732,10 +732,12 @@ EXTRA_DIST += \ TESTS += \ test-file.sh \ test-file-readonly.sh \ + test-file-fd.sh \ $(NULL) EXTRA_DIST += \ test-file.sh \ test-file-readonly.sh \ + test-file-fd.sh \ $(NULL) LIBGUESTFS_TESTS += test-file-block diff --git a/plugins/file/file.c b/plugins/file/file.c index f673ec132..4e41e738a 100644 --- a/plugins/file/file.c +++ b/plugins/file/file.c @@ -70,9 +70,15 @@ #include "isaligned.h" #include "fdatasync.h" -static enum { mode_none, mode_filename, mode_directory } mode = mode_none; +static enum { + mode_none, + mode_filename, + mode_directory, + mode_filedesc, +} mode = mode_none; static char *filename = NULL; static char *directory = NULL; +static int filedesc = -1; /* posix_fadvise mode: -1 = don't set it, or POSIX_FADV_*. */ static int fadvise_mode = @@ -184,7 +190,7 @@ file_config (const char *key, const char *value) if (mode != mode_none) { wrong_mode: nbdkit_error ("%s parameter can only appear once on the command line", - "file|dir"); + "file|dir|fd"); return -1; } mode = mode_filename; @@ -202,6 +208,17 @@ file_config (const char *key, const char *value) if (!directory) return -1; } + else if (strcmp (key, "fd") == 0) { + if (mode != mode_none) goto wrong_mode; + mode = mode_filedesc; + assert (filedesc == -1); + if (nbdkit_parse_int ("fd", value, &filedesc) == -1) + return -1; + if (filedesc <= 2) { + nbdkit_error ("file descriptor must be >= 3"); + return -1; + } + } else if (strcmp (key, "fadvise") == 0) { /* As this is a hint, if the kernel doesn't support the feature * ignore the parameter. @@ -263,18 +280,26 @@ file_config_complete (void) struct stat sb; if (mode == mode_none) { - nbdkit_error ("you must supply either [file=]<FILENAME> or " - "dir=<DIRNAME> parameter after the plugin name " + nbdkit_error ("you must supply [file=]<FILENAME>, " + "dir=<DIRNAME> or fd=<FD> " + "parameter after the plugin name " "on the command line"); return -1; } if (mode == mode_filename) { assert (filename != NULL); assert (directory == NULL); + assert (filedesc == -1); } if (mode == mode_directory) { assert (filename == NULL); assert (directory != NULL); + assert (filedesc == -1); + } + if (mode == mode_filedesc) { + assert (filename == NULL); + assert (directory == NULL); + assert (filedesc >= 3); } /* Sanity check now, rather than waiting for first client open. @@ -299,6 +324,8 @@ file_config_complete (void) return -1; } break; + case mode_filedesc: + break; default: abort (); } @@ -341,6 +368,7 @@ file_list_exports (int readonly, int default_only, switch (mode) { case mode_filename: + case mode_filedesc: return nbdkit_add_export (exports, "", NULL); case mode_directory: @@ -408,59 +436,69 @@ file_open (int readonly) const char *file; int dfd = -1; + h = malloc (sizeof *h); + if (h == NULL) { + nbdkit_error ("malloc: %m"); + return NULL; + } + h->can_write = !readonly; + h->fd = -1; + switch (mode) { case mode_directory: file = nbdkit_export_name (); if (strchr (file, '/')) { nbdkit_error ("exportname cannot contain /"); + free (h); errno = EINVAL; return NULL; } dfd = open (directory, O_RDONLY | O_DIRECTORY | O_CLOEXEC); if (dfd == -1) { nbdkit_error ("open %s: %m", directory); + free (h); return NULL; } break; case mode_filename: file = filename; break; + case mode_filedesc: + h->fd = dup (filedesc); + if (h->fd == -1) { + nbdkit_error ("dup fd=%d: %m", filedesc); + free (h); + return NULL; + } + file = "<file descriptor>"; /* This is needed for error messages. */ + break; default: abort (); } - h = malloc (sizeof *h); - if (h == NULL) { - nbdkit_error ("malloc: %m"); - if (dfd != -1) - close (dfd); - return NULL; - } - - flags = O_CLOEXEC|O_NOCTTY; - if (readonly) { - flags |= O_RDONLY; - h->can_write = false; - } - else { - flags |= O_RDWR; - h->can_write = true; - } - - h->fd = openat (dfd, file, flags); - if (h->fd == -1 && !readonly) { - nbdkit_debug ("open O_RDWR failed, falling back to read-only: %s: %m", - file); - flags = (flags & ~O_ACCMODE) | O_RDONLY; - h->fd = openat (dfd, file, flags); - h->can_write = false; - } if (h->fd == -1) { - nbdkit_error ("open: %s: %m", file); - if (dfd != -1) - close (dfd); - free (h); - return NULL; + flags = O_CLOEXEC|O_NOCTTY; + if (readonly) + flags |= O_RDONLY; + else + flags |= O_RDWR; + + h->fd = openat (dfd, file, flags); + if (h->fd == -1 && !readonly) { + nbdkit_debug ("open O_RDWR failed, falling back to read-only: %s: %m", + file); + flags = (flags & ~O_ACCMODE) | O_RDONLY; + h->fd = openat (dfd, file, flags); + h->can_write = false; + } + if (h->fd == -1) { + nbdkit_error ("open: %s: %m", file); + if (dfd != -1) + close (dfd); + free (h); + return NULL; + } } + if (dfd != -1) close (dfd); diff --git a/tests/test-file-fd.sh b/tests/test-file-fd.sh new file mode 100755 index 000000000..6c98ad9e5 --- /dev/null +++ b/tests/test-file-fd.sh @@ -0,0 +1,65 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright (C) 2013-2022 Red Hat Inc. +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test the file plugin fd parameter. + +source ./functions.sh +set -e +set -x + +requires_plugin file +requires_nbdsh_uri +requires $TRUNCATE --version + +sock=$(mktemp -u /tmp/nbdkit-test-sock.XXXXXX) +files="file-fd.pid file-fd.img $sock" +rm -f $files +cleanup_fn rm -f $files + +$TRUNCATE -s 16384 file-fd.img +exec 6<>file-fd.img +start_nbdkit -P file-fd.pid -U $sock file fd=6 + +nbdsh -u "nbd+unix://?socket=$sock" -c ' +assert not h.is_read_only() +assert h.get_size() == 16384 + +buf0 = bytearray(1024) +buf1 = b"1" * 1024 +buf2 = b"2" * 1024 +h.pwrite(buf1 + buf2 + buf1 + buf2, 1024) +buf = h.pread(8192, 0) +assert buf == buf0 + buf1 + buf2 + buf1 + buf2 + buf0*3 +h.zero(4096, 1024) +buf = h.pread(8192, 0) +assert buf == buf0*8 +' -- 2.37.0.rc2