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dissect: add a mode for operating on an in-memory copy of a DDI, instead of directly on it

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This is useful for operating in ephemeral, writable mode on any image,
including read-only ones. It also has the benefit of not keeping the
image file's filesystem busy.

Inspired by the discussions in #25648
This commit is contained in:
Lennart Poettering
2022-12-08 12:46:09 +01:00
parent fcd8a19da8
commit 6c07d57075
1 changed files with 17 additions and 7 deletions
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24
src/dissect/dissect.c
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@@ -77,6 +77,7 @@ static JsonFormatFlags arg_json_format_flags = JSON_FORMAT_OFF;
static PagerFlags arg_pager_flags = 0;
static bool arg_legend = true;
static bool arg_rmdir = false;
static bool arg_in_memory = false;
static char **arg_argv = NULL;
STATIC_DESTRUCTOR_REGISTER(arg_verity_settings, verity_settings_done);
@@ -108,6 +109,7 @@ static int help(void) {
" --mkdir Make mount directory before mounting, if missing\n"
" --rmdir Remove mount directory after unmounting\n"
" --discard=MODE Choose 'discard' mode (disabled, loop, all, crypto)\n"
" --in-memory Copy image into memory\n"
" --root-hash=HASH Specify root hash for verity\n"
" --root-hash-sig=SIG Specify pkcs7 signature of root hash for verity\n"
" as a DER encoded PKCS7, either as a path to a file\n"
@@ -200,6 +202,7 @@ static int parse_argv(int argc, char *argv[]) {
ARG_VERITY_DATA,
ARG_MKDIR,
ARG_RMDIR,
ARG_IN_MEMORY,
ARG_JSON,
ARG_MTREE,
ARG_DISCOVER,
@@ -222,6 +225,7 @@ static int parse_argv(int argc, char *argv[]) {
{ "verity-data", required_argument, NULL, ARG_VERITY_DATA },
{ "mkdir", no_argument, NULL, ARG_MKDIR },
{ "rmdir", no_argument, NULL, ARG_RMDIR },
{ "in-memory", no_argument, NULL, ARG_IN_MEMORY },
{ "list", no_argument, NULL, 'l' },
{ "mtree", no_argument, NULL, ARG_MTREE },
{ "copy-from", no_argument, NULL, 'x' },
@@ -340,6 +344,10 @@ static int parse_argv(int argc, char *argv[]) {
break;
}
case ARG_IN_MEMORY:
arg_in_memory = true;
break;
case ARG_ROOT_HASH: {
_cleanup_free_ void *p = NULL;
size_t l;
@@ -1392,7 +1400,8 @@ static int action_discover(void) {
static int run(int argc, char *argv[]) {
_cleanup_(dissected_image_unrefp) DissectedImage *m = NULL;
_cleanup_(loop_device_unrefp) LoopDevice *d = NULL;
int r;
uint32_t loop_flags;
int open_flags, r;
log_setup();
@@ -1417,12 +1426,13 @@ static int run(int argc, char *argv[]) {
* available we turn off partition table
* support */
r = loop_device_make_by_path(
arg_image,
FLAGS_SET(arg_flags, DISSECT_IMAGE_DEVICE_READ_ONLY) ? O_RDONLY : O_RDWR,
FLAGS_SET(arg_flags, DISSECT_IMAGE_NO_PARTITION_TABLE) ? 0 : LO_FLAGS_PARTSCAN,
LOCK_SH,
&d);
open_flags = FLAGS_SET(arg_flags, DISSECT_IMAGE_DEVICE_READ_ONLY) ? O_RDONLY : O_RDWR;
loop_flags = FLAGS_SET(arg_flags, DISSECT_IMAGE_NO_PARTITION_TABLE) ? 0 : LO_FLAGS_PARTSCAN;
if (arg_in_memory)
r = loop_device_make_by_path_memory(arg_image, open_flags, loop_flags, LOCK_SH, &d);
else
r = loop_device_make_by_path(arg_image, open_flags, loop_flags, LOCK_SH, &d);
if (r < 0)
return log_error_errno(r, "Failed to set up loopback device for %s: %m", arg_image);