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LibCore/Userland: Introduce a simple tail implementation

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Also introduce more seek modes on CIODevice, and an out param to find
the current position inside the file -- this means less syscalls (and
less potential races) than requesting it through a separate pos()
accessor or something.
This commit is contained in:
Robin Burchell 2019-05-16 15:02:17 +02:00 • committed by Andreas Kling
parent 805e87a21c
commit c8fda23a03
3 changed files with 143 additions and 4 deletions
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22
LibCore/CIODevice.cpp
View file

@ -174,15 +174,31 @@ bool CIODevice::close()
return true;
}
bool CIODevice::seek(signed_qword offset)
bool CIODevice::seek(signed_qword offset, SeekMode mode, off_t *pos)
{
int rc = lseek(m_fd, offset, SEEK_SET);
int m = SEEK_SET;
switch (mode) {
case SeekMode::SetPosition:
m = SEEK_SET;
break;
case SeekMode::FromCurrentPosition:
m = SEEK_CUR;
break;
case SeekMode::FromEndPosition:
m = SEEK_END;
break;
}
off_t rc = lseek(m_fd, offset, m);
if (rc < 0) {
perror("CIODevice::seek: lseek");
set_error(errno);
if (pos)
*pos = -1;
return false;
}
m_buffered_data.clear();
m_eof = false;
if (pos)
*pos = rc;
return true;
}

8
LibCore/CIODevice.h
View file

@ -37,7 +37,13 @@ public:
bool can_read() const;
bool seek(signed_qword);
enum class SeekMode {
SetPosition,
FromCurrentPosition,
FromEndPosition,
};
bool seek(signed_qword, SeekMode = SeekMode::SetPosition, off_t* = nullptr);
virtual bool open(CIODevice::OpenMode) = 0;
virtual bool close();