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os/vfs.h: read loop in Readonly_file::read

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This patch improves the Readonly_file::read method such that the
capacity of the specified buffer is used as upper bound for the read
operation instead of VFS-internal I/O buffer sizes. This relieves the
caller from implementing a read loop in most cases.

As a step away from C-ish use of the API, the patch deprecates the old
'read' method that takes the buffer as char *, size_t arguments.

Fixes #4745
This commit is contained in:
Norman Feske 2023-01-27 20:06:02 +01:00 committed by Christian Helmuth
parent 345b77cfc9
commit 61a7671de1
1 changed files with 58 additions and 44 deletions
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102
repos/os/include/os/vfs.h
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@ -289,14 +289,17 @@ struct Genode::Directory : Noncopyable, Interface
auto open_res = _nonconst_fs().openlink(
join(_path, rel_path).string(),
false, &link_handle, _alloc);
if (open_res != Directory_service::OPENLINK_OK)
throw Nonexistent_file();
Vfs_handle::Guard guard(link_handle);
char buf[MAX_PATH_LEN];
Vfs::file_size count = sizeof(buf)-1;
Vfs::file_size out_count = 0;
while (!link_handle->fs().queue_read(link_handle, count)) {
_io.commit_and_wait();
}
@ -452,50 +455,71 @@ class Genode::Readonly_file : public File
struct At { Vfs::file_size value; };
/**
* Read number of 'bytes' from file into local memory buffer 'dst'
*
* \throw Truncated_during_read
* Read file content starting at 'at' into byte buffer 'range'
*/
size_t read(At at, char *dst, size_t bytes) const
size_t read(At at, Byte_range_ptr const &range) const
{
Vfs::file_size out_count = 0;
_handle->seek(at.value);
while (!_handle->fs().queue_read(_handle, bytes))
_io.commit_and_wait();
Vfs::File_io_service::Read_result result;
size_t total = 0;
for (;;) {
result = _handle->fs().complete_read(_handle, dst, bytes,
out_count);
if (result != Vfs::File_io_service::READ_QUEUED)
_handle->seek(at.value + total);
while (!_handle->fs().queue_read(_handle, range.num_bytes))
_io.commit_and_wait();
Vfs::File_io_service::Read_result result;
Vfs::file_size read_bytes { }; /* byte count for this iteration */
for (;;) {
result = _handle->fs().complete_read(_handle,
range.start + total,
range.num_bytes - total,
read_bytes);
if (result != Vfs::File_io_service::READ_QUEUED)
break;
_io.commit_and_wait();
};
if (read_bytes > range.num_bytes - total) {
error("read beyond buffer size");
break;
}
if (read_bytes == 0)
break;
_io.commit_and_wait();
};
total += size_t(read_bytes);
}
/*
* XXX handle READ_ERR_WOULD_BLOCK, READ_QUEUED
*/
return total;
}
if (result != Vfs::File_io_service::READ_OK)
throw Truncated_during_read();
/*
* \deprecated use 'Byte_range_ptr'
*/
size_t read(char *dst, size_t bytes) const __attribute__((deprecated))
{
return read(At{0}, Byte_range_ptr(dst, bytes));
}
return (size_t)out_count;
/*
* \deprecated use 'Byte_range_ptr'
*/
size_t read(At at, char *dst, size_t bytes) const __attribute__((deprecated))
{
return read(at, Byte_range_ptr(dst, bytes));
}
/**
* Read number of 'bytes' from the start of the file into local memory
* buffer 'dst'
*
* \throw Truncated_during_read
* Read file content into byte buffer 'range'
*/
size_t read(char *dst, size_t bytes) const
size_t read(Byte_range_ptr const &range) const
{
return read(At{0}, dst, bytes);
return read(At{0}, range);
}
};
@ -504,6 +528,8 @@ class Genode::Readonly_file : public File
* Call functor 'fn' with the data pointer and size in bytes
*
* If the buffer has a size of zero, 'fn' is not called.
*
* \throw Truncated_during_read
*/
template <typename FN>
void Genode::with_raw_file_content(Readonly_file const &file,
@ -512,19 +538,7 @@ void Genode::with_raw_file_content(Readonly_file const &file,
if (range.num_bytes == 0)
return;
size_t total_read = 0;
while (total_read < range.num_bytes) {
size_t read_bytes = file.read(Readonly_file::At{total_read},
range.start + total_read,
range.num_bytes - total_read);
if (read_bytes == 0)
break;
total_read += read_bytes;
}
if (total_read != range.num_bytes)
if (file.read(range) != range.num_bytes)
throw File::Truncated_during_read();
fn(range.start, range.num_bytes);
@ -541,8 +555,8 @@ template <typename FN>
void Genode::with_xml_file_content(Readonly_file const &file,
Byte_range_ptr const &range, FN const &fn)
{
with_raw_file_content(file, range,
[&] (char const *ptr, size_t num_bytes) {
with_raw_file_content(file, range, [&] (char const *ptr, size_t num_bytes) {
try {
fn(Xml_node(ptr, num_bytes));
return;