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gems/vfs.h: intuitive meaning of 'Directory const'

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With this patch, it becomes possible to pass a 'Directory const &' to
the constructor of 'File_content', which is intuitive as the directory
content is not changed by reading a file.
This commit is contained in:
Norman Feske 2017-12-18 14:06:06 +01:00 committed by Christian Helmuth
parent 75e22fef4a
commit f5fb9684db
1 changed files with 38 additions and 4 deletions
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42
repos/gems/include/gems/vfs.h
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@ -179,11 +179,23 @@ struct Genode::Directory : Noncopyable
}
}
template <typename FN>
void for_each_entry(FN const &fn) const
{
auto const_fn = [&] (Entry const &e) { fn(e); };
const_cast<Directory &>(*this).for_each_entry(const_fn);
}
bool file_exists(Path const &rel_path) const
{
return _stat(rel_path).mode & Vfs::Directory_service::STAT_MODE_FILE;
}
bool directory_exists(Path const &rel_path) const
{
return _stat(rel_path).mode & Vfs::Directory_service::STAT_MODE_DIRECTORY;
}
/**
* Return size of file at specified directory-relative path
*
@ -249,6 +261,27 @@ class Genode::Readonly_file : public File
}
}
/**
* Strip off constness of 'Directory const &'
*
* Since the 'Readonly_file' API provides an abstraction over the
* low-level VFS operations, the intuitive meaning of 'const' is
* different between the 'Readonly_file' API and the VFS.
*
* At the VFS level, opening a file changes the internal state of the
* VFS. Hence the operation is non-const. However, the user of the
* 'Readonly_file' API expects the constness of a directory to
* correspond to whether the directory can be modified or not. In the
* case of instantiating a 'Readonly_file', one would expect that a
* 'Directory const &' would suffice. The fact that - under the hood -
* the 'Readonly_file' has to perform the nonconst 'open' operation at
* the VFS is of not of interest.
*/
static Directory &_mutable(Directory const &dir)
{
return const_cast<Directory &>(dir);
}
public:
/**
@ -256,10 +289,11 @@ class Genode::Readonly_file : public File
*
* \throw File::Open_failed
*/
Readonly_file(Directory &dir, Path const &rel_path)
: _ep(dir._ep)
Readonly_file(Directory const &dir, Path const &rel_path)
: _ep(_mutable(dir)._ep)
{
_open(dir._fs, dir._alloc, Path(dir._path, "/", rel_path));
_open(_mutable(dir)._fs, _mutable(dir)._alloc,
Path(dir._path, "/", rel_path));
}
~Readonly_file() { _handle->ds().close(_handle); }
@ -325,7 +359,7 @@ class Genode::File_content
* \throw Truncated_during_read number of readable bytes differs
* from file status information
*/
File_content(Allocator &alloc, Directory &dir, Path const &rel_path,
File_content(Allocator &alloc, Directory const &dir, Path const &rel_path,
Limit limit)
:
_alloc(alloc),