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Kernel: Improve ProcFS behavior in low memory conditions

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When ProcFS could no longer allocate KBuffer objects to serve calls to
read, it would just return 0, indicating EOF. This then triggered
parsing errors because code assumed it read the file.

Because read isn't supposed to return ENOMEM, change ProcFS to populate
the file data upon file open or seek to the beginning. This also means
that calls to open can now return ENOMEM if needed. This allows the
caller to either be able to successfully open the file and read it, or
fail to open it in the first place.
This commit is contained in:
Tom 2020-09-17 13:51:09 -06:00 • committed by Andreas Kling
parent b36f57e570
commit f98ca35b83
24 changed files with 398 additions and 243 deletions
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12
Kernel/FileSystem/ProcFS.h
View file

@ -30,7 +30,7 @@
#include <AK/Types.h>
#include <Kernel/FileSystem/FileSystem.h>
#include <Kernel/FileSystem/Inode.h>
#include <Kernel/KBuffer.h>
#include <Kernel/KBufferBuilder.h>
#include <Kernel/Lock.h>
namespace Kernel {
@ -59,7 +59,7 @@ private:
struct ProcFSDirectoryEntry {
ProcFSDirectoryEntry() { }
ProcFSDirectoryEntry(const char* a_name, unsigned a_proc_file_type, bool a_supervisor_only, OwnPtr<KBuffer> (*read_callback)(InodeIdentifier) = nullptr, ssize_t (*write_callback)(InodeIdentifier, const UserOrKernelBuffer&, size_t) = nullptr, RefPtr<ProcFSInode>&& a_inode = nullptr)
ProcFSDirectoryEntry(const char* a_name, unsigned a_proc_file_type, bool a_supervisor_only, bool (*read_callback)(InodeIdentifier, KBufferBuilder&) = nullptr, ssize_t (*write_callback)(InodeIdentifier, const UserOrKernelBuffer&, size_t) = nullptr, RefPtr<ProcFSInode>&& a_inode = nullptr)
: name(a_name)
, proc_file_type(a_proc_file_type)
, supervisor_only(a_supervisor_only)
@ -72,7 +72,7 @@ private:
const char* name { nullptr };
unsigned proc_file_type { 0 };
bool supervisor_only { false };
OwnPtr<KBuffer> (*read_callback)(InodeIdentifier);
bool (*read_callback)(InodeIdentifier, KBufferBuilder&);
ssize_t (*write_callback)(InodeIdentifier, const UserOrKernelBuffer&, size_t);
RefPtr<ProcFSInode> inode;
InodeIdentifier identifier(unsigned fsid) const;
@ -96,6 +96,8 @@ public:
private:
// ^Inode
virtual KResult attach(FileDescription&) override;
virtual void did_seek(FileDescription&, off_t) override;
virtual ssize_t read_bytes(off_t, ssize_t, UserOrKernelBuffer& buffer, FileDescription*) const override;
virtual InodeMetadata metadata() const override;
virtual KResult traverse_as_directory(Function<bool(const FS::DirectoryEntryView&)>) const override;
@ -110,6 +112,8 @@ private:
virtual KResult chown(uid_t, gid_t) override;
virtual KResultOr<NonnullRefPtr<Custody>> resolve_as_link(Custody& base, RefPtr<Custody>* out_parent = nullptr, int options = 0, int symlink_recursion_level = 0) const override;
KResult refresh_data(FileDescription&) const;
ProcFS& fs() { return static_cast<ProcFS&>(Inode::fs()); }
const ProcFS& fs() const { return static_cast<const ProcFS&>(Inode::fs()); }
ProcFSInode(ProcFS&, unsigned index);
@ -123,6 +127,8 @@ public:
private:
// ^Inode
virtual KResult attach(FileDescription&) override;
virtual void did_seek(FileDescription&, off_t) override;
virtual ssize_t read_bytes(off_t, ssize_t, UserOrKernelBuffer&, FileDescription*) const override { ASSERT_NOT_REACHED(); }
virtual InodeMetadata metadata() const override;
virtual KResult traverse_as_directory(Function<bool(const FS::DirectoryEntryView&)>) const override { ASSERT_NOT_REACHED(); }