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Workaround bad JSON output from sfdisk. 

The output of `sfdisk --json /dev/sdb` is not necessarily
valid JSON. Then, no partition information is stored,
no first-valid-lba in particular. This leads to new partitions
being made from sector 0, which is invalid on a GPT table.

The workaround is to manually fix the known-broken JSON
from sfdisk. This is amply documented in a standalone
static function.

FIXES #425097
This commit is contained in:
Adriaan de Groot 2020-08-24 22:53:54 +02:00
parent 394859444f
commit 6aa9d93728
1 changed files with 56 additions and 1 deletions
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57
src/plugins/sfdisk/sfdiskbackend.cpp
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@ -126,6 +126,58 @@ QList<Device*> SfdiskBackend::scanDevices(const ScanFlags scanFlags)
return result;
}
/*** @brief Fix up bogus JSON from `sfdisk --json /dev/sdb`
*
* The command `sfdisk --json /dev/sdb` outputs a JSON representation
* of the partition table, with general device characteristics and
* the list of partitions, **but**..
*
* This isn't necessarily valid JSON: in particular, when there are
* no partitions on the disk because it is empty / was recently zeroed /
* is a USB stick for testing purposes, the output is changed **only**
* by there being no partitions in the partition table. However,
* the comma (",") after sectorsize is still printed. Bogus output looks
* like this:
*
* {
* "partitiontable": {
* "label":"gpt",
* "id":"1F9E80D9-DD78-024F-94A3-B61EC82B18C8",
* "device":"/dev/sdb",
* "unit":"sectors",
* "firstlba":2048,
* "lastlba":30949342,
* "sectorsize":512,
* }
* }
*
* That's not valid JSON because of the "," followed by nothing until
* the brace, and yields an empty object is passed to fromJson().
*
* We'll go through and check if there's a "," followed by whitespace
* and then a }. If there is, replace the ,.
*/
static void
removeCommaFollowedByBrace( QByteArray& s )
{
// -1 if there is no comma (but then there's no useful JSON either),
// not is 0 a valid place (the start) for a , in a JSON document.
int lastComma = s.lastIndexOf(',');
if ( lastComma > 0 )
{
for ( int charIndex = lastComma + 1; charIndex < s.length(); ++charIndex )
{
if ( s[charIndex] == '}' )
{
s[lastComma] = ' '; // Erase that comma
}
if ( !isspace( s[charIndex] ) )
{
break;
}
}
}
}
/** Create a Device for the given device_node and scan it for partitions.
@param deviceNode the device node (e.g. "/dev/sda")
@ -207,7 +259,10 @@ Device* SfdiskBackend::scanDevice(const QString& deviceNode)
if (jsonCommand.exitCode() != 0)
return d;
const QJsonObject jsonObject = QJsonDocument::fromJson(jsonCommand.rawOutput()).object();
auto s = jsonCommand.rawOutput();
fixInvalidJsonFromSFDisk(s);
const QJsonObject jsonObject = QJsonDocument::fromJson(s).object();
const QJsonObject partitionTable = jsonObject[QLatin1String("partitiontable")].toObject();
if (!updateDevicePartitionTable(*d, partitionTable))