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Add io_pread().

It will be used by --list.
This commit is contained in:
Lasse Collin 2010-01-24 22:46:11 +02:00
parent ef68dd4a92
commit df254ce03b
2 changed files with 42 additions and 0 deletions

View file

@ -812,6 +812,31 @@ io_read(file_pair *pair, io_buf *buf_union, size_t size)
}
extern bool
io_pread(file_pair *pair, io_buf *buf, size_t size, off_t pos)
{
// Using lseek() and read() is more portable than pread() and
// for us it is as good as real pread().
if (lseek(pair->src_fd, pos, SEEK_SET) != pos) {
message_error(_("%s: Error seeking the file: %s"),
pair->src_name, strerror(errno));
return true;
}
const size_t amount = io_read(pair, buf, size);
if (amount == SIZE_MAX)
return true;
if (amount != size) {
message_error(_("%s: Unexpected end of file"),
pair->src_name);
return true;
}
return false;
}
static bool
is_sparse(const io_buf *buf)
{

View file

@ -23,6 +23,7 @@
/// Use an union to make sure that the buffer is properly aligned.
typedef union {
uint8_t u8[IO_BUFFER_SIZE];
uint32_t u32[IO_BUFFER_SIZE / sizeof(uint32_t)];
uint64_t u64[IO_BUFFER_SIZE / sizeof(uint64_t)];
} io_buf;
@ -97,6 +98,22 @@ extern void io_close(file_pair *pair, bool success);
extern size_t io_read(file_pair *pair, io_buf *buf, size_t size);
/// \brief Read from source file from given offset to a buffer
///
/// This is remotely similar to standard pread(). This uses lseek() though,
/// so the read offset is changed on each call.
///
/// \param pair Seekable source file
/// \param buf Destination buffer
/// \param size Amount of data to read
/// \param pos Offset relative to the beginning of the file,
/// from which the data should be read.
///
/// \return On success, false is returned. On error, error message
/// is printed and true is returned.
extern bool io_pread(file_pair *pair, io_buf *buf, size_t size, off_t pos);
/// \brief Writes a buffer to the destination file
///
/// \param pair File pair having the destination file open for writing