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QStorageInfo/Linux: resolve non-existent devices via /dev/block

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On systems with very simple boot sequences, the kernel will create a
device called /dev/root and use that to mount the root filesystem.
However, that doesn't actually exist in /dev and could cause
confusion. So we try to resolve using /dev/block if the /dev entry does
not exist but udev is in use (udevd has the string "/dev/%s/%u:%u").

[ChangeLog][QtCore][QStorageInfo] Improved discovery of device nodes on
Linux if the /dev entry was renamed after the filesystem was mounted and
udev is in use.

Fixes: QTBUG-81464
Change-Id: If79a52e476594446baccfffd15eec573ae3deb0d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Thiago Macieira 2020-01-30 12:53:39 -08:00
parent 6b9a1824a4
commit 23d42a6a30
1 changed files with 18 additions and 3 deletions
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21
src/corelib/io/qstorageinfo_unix.cpp
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@ -60,6 +60,7 @@
#elif defined(Q_OS_LINUX) || defined(Q_OS_HURD)
# include <mntent.h>
# include <sys/statvfs.h>
# include <sys/sysmacros.h>
#elif defined(Q_OS_SOLARIS)
# include <sys/mnttab.h>
# include <sys/statvfs.h>
@ -152,7 +153,7 @@ private:
//(2) parent ID: the ID of the parent mount (or of self for the top of the mount tree).
// int parent_id;
//(3) major:minor: the value of st_dev for files on this filesystem (see stat(2)).
// dev_t rdev;
dev_t rdev;
//(4) root: the pathname of the directory in the filesystem which forms the root of this mount.
char *subvolume;
//(5) mount point: the pathname of the mount point relative to the process's root directory.
@ -503,8 +504,7 @@ inline bool QStorageIterator::next()
int rdevminor = qstrtoll(ptr + 1, const_cast<const char **>(&ptr), 10, &ok);
if (!ptr || !ok)
return false;
Q_UNUSED(rdevmajor);
Q_UNUSED(rdevminor);
mnt.rdev = makedev(rdevmajor, rdevminor);
if (*ptr != ' ')
return false;
@ -566,6 +566,21 @@ inline QByteArray QStorageIterator::fileSystemType() const
inline QByteArray QStorageIterator::device() const
{
// check that the device exists
if (mnt.mnt_fsname[0] == '/' && access(mnt.mnt_fsname, F_OK) != 0) {
// It doesn't, so let's try to resolve the dev_t from /dev/block.
// Note how strlen("4294967295") == digits10 + 1, so we need to add 1
// for each number, plus the ':'.
char buf[sizeof("/dev/block/") + 2 * std::numeric_limits<unsigned>::digits10 + 3];
QByteArray dev(PATH_MAX, Qt::Uninitialized);
char *devdata = dev.data();
snprintf(buf, sizeof(buf), "/dev/block/%u:%u", major(mnt.rdev), minor(mnt.rdev));
if (realpath(buf, devdata)) {
dev.truncate(strlen(devdata));
return dev;
}
}
return QByteArray(mnt.mnt_fsname);
}