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-rw-r--r--src/xz/file_io.c25
-rw-r--r--src/xz/file_io.h17
2 files changed, 42 insertions, 0 deletions
diff --git a/src/xz/file_io.c b/src/xz/file_io.c
index d94e2321..a07501c1 100644
--- a/src/xz/file_io.c
+++ b/src/xz/file_io.c
@@ -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)
{
diff --git a/src/xz/file_io.h b/src/xz/file_io.h
index 58bf7b5e..94d4c174 100644
--- a/src/xz/file_io.h
+++ b/src/xz/file_io.h
@@ -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