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libc: fix cached ioctl info file access

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This patch solves the false-negative error message "failed to open file"
referring to an ioctl info file during an ioctl call. The message is
now avoided by checking for the existence of the file before reading it.

However, the observed symptom uncovered an actual bug that was
introduced in commit "libc vfs: open OSS 'info' file only once" with
the attempt to cache the content of ioctl info files. When called
multiple time for different paths, 'Vfs_plugin::_with_info' would
wrongly return the info from the first call as cached in a local
static variable.

The patch fixes the problem by a new added 'Cached_ioctl_info'
implementation in the scope of the 'Vfs_plugin'.

Issue #4372
Fixes #4852
This commit is contained in:
Norman Feske 2023-05-03 12:29:18 +02:00 committed by Checker
parent 2e76374a35
commit 0e3a9bfe1f
2 changed files with 39 additions and 13 deletions
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33
repos/libports/src/lib/libc/internal/vfs_plugin.h
View File

@ -93,6 +93,39 @@ class Libc::Vfs_plugin final : public Plugin
bool const _pipe_configured;
Registry<Mmap_entry> _mmap_registry;
/*
* Cache the latest info file to accomodate highly frequent 'ioctl'
* calls as observed by the OSS plugin.
*/
struct Cached_ioctl_info : Noncopyable
{
Vfs_plugin &_vfs_plugin;
Constructible<Readonly_file> _file { };
Absolute_path _path { };
template <typename FN>
void with_file(Absolute_path const &path, FN const &fn)
{
if (!_vfs_plugin._root_dir.constructed()) {
warning("Vfs_plugin::_root_dir unexpectedly not constructed");
return;
}
Directory &root_dir = *_vfs_plugin._root_dir;
if (path != _path && root_dir.file_exists(path.string())) {
_file.construct(root_dir, path);
_path = path;
}
if (path == _path && _file.constructed())
fn(*_file);
}
Cached_ioctl_info(Vfs_plugin &vfs_plugin) : _vfs_plugin(vfs_plugin) { }
} _cached_ioctl_info { *this };
/**
* Sync a handle
*/

19
repos/libports/src/lib/libc/vfs_plugin.cc
View File

@ -239,26 +239,19 @@ namespace Libc {
template <typename FN>
void Libc::Vfs_plugin::_with_info(File_descriptor &fd, FN const &fn)
{
if (!_root_dir.constructed())
return;
Absolute_path path = ioctl_dir(fd);
path.append_element("info");
try {
/*
* Opening the info file repeatedly could be too expensive if
* file system servers are part of the VFS, because the directory
* status of the path would be checked at each VFS plugin every
* time. So, we open the file only once.
*/
static Readonly_file file { *_root_dir, path.string() };
static char buffer[4096];
_cached_ioctl_info.with_file(path, [&] (Readonly_file const &file) {
char buffer[4096] { };
Byte_range_ptr range(buffer,
min((size_t)(_root_dir->file_size(path.string())),
sizeof(buffer)));
with_xml_file_content(file, range, [&] (Xml_node node) { fn(node); });
} catch (...) { }
});
}