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For sparse output, instead of fstat(), ftruncate(), then lseek(), do lseek() then ftruncate(), like dd does (#45).

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This commit is contained in:
Andrew Wood
2025-10-14 23:38:15 +01:00
parent 72686655cf
commit c21ad6fdf1
1 changed files with 9 additions and 16 deletions
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src/pv/transfer.c
+9 -16
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@@ -656,7 +656,7 @@ static int pv__transfer_write(pvstate_t state, bool *eof_in, bool *eof_out, long
ssize_t nwritten;
int write_errno;
bool all_nulls;
struct stat sb;
off_t output_offset;
size_t write_check_position, write_end_position;
if (NULL == state->transfer.transfer_buffer) {
@@ -693,32 +693,25 @@ static int pv__transfer_write(pvstate_t state, bool *eof_in, bool *eof_out, long
if (all_nulls) {
/*
* Get the current size of the output file,
* so we can attempt to enlarge it with
* ftruncate() and then use lseek() to skip
* to the new end of the file.
* Use lseek() to move forward in the file,
* and then ftruncate() it to its new size.
*
* If any step fails, mark the output not
* seekable so we stop trying.
*/
memset(&sb, 0, sizeof(sb));
/*@+longintegral@ */
/*
* splint has trouble with off_t / __off_t, in the lseek() call.
*/
if (0 != fstat(state->control.output_fd, &sb)) {
debug("%s: %s", "output fstat() failed", strerror(errno));
state->transfer.output_not_seekable = true;
} else if (0 !=
ftruncate(state->control.output_fd,
sb.st_size + (off_t) (state->transfer.to_write))) {
debug("%s: %s", "output ftruncate() failed", strerror(errno));
state->transfer.output_not_seekable = true;
} else if (lseek(state->control.output_fd, (off_t) (state->transfer.to_write), SEEK_CUR)
== (off_t) - 1) {
output_offset =
lseek(state->control.output_fd, (off_t) (state->transfer.to_write), SEEK_CUR);
if (output_offset == (off_t) - 1) {
debug("%s: %s", "output lseek() failed", strerror(errno));
state->transfer.output_not_seekable = true;
} else if (0 != ftruncate(state->control.output_fd, output_offset)) {
debug("%s: %s", "output ftruncate() failed", strerror(errno));
state->transfer.output_not_seekable = true;
} else {
/* Seek successful - skip write. */
nwritten = state->transfer.to_write;