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Move pg_pwritev_with_retry() to src/common/file_utils.c

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This commit moves pg_pwritev_with_retry(), a convenience wrapper of
pg_writev() able to handle partial writes, to common/file_utils.c so
that the frontend code is able to use it.  A first use-case targetted
for this routine is pg_basebackup and pg_receivewal, for the
zero-padding of a newly-initialized WAL segment.  This is used currently
in the backend when the GUC wal_init_zero is enabled (default).

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Thomas Munro
Discussion: https://postgr.es/m/CALj2ACUq7nAb7=bJNbK3yYmp-SZhJcXFR_pLk8un6XgDzDF3OA@mail.gmail.com
This commit is contained in:
Michael Paquier
2022-10-27 14:39:42 +09:00
parent 1b9cd69c5b
commit 4ab8c81bd9
4 changed files with 74 additions and 71 deletions
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65
src/backend/storage/file/fd.c
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@ -93,7 +93,6 @@
#include "common/pg_prng.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "port/pg_iovec.h"
#include "portability/mem.h"
#include "postmaster/startup.h"
#include "storage/fd.h"
@ -3738,67 +3737,3 @@ data_sync_elevel(int elevel)
{
return data_sync_retry ? elevel : PANIC;
}
/*
* A convenience wrapper for pg_pwritev() that retries on partial write. If an
* error is returned, it is unspecified how much has been written.
*/
ssize_t
pg_pwritev_with_retry(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
struct iovec iov_copy[PG_IOV_MAX];
ssize_t sum = 0;
ssize_t part;
/* We'd better have space to make a copy, in case we need to retry. */
if (iovcnt > PG_IOV_MAX)
{
errno = EINVAL;
return -1;
}
for (;;)
{
/* Write as much as we can. */
part = pg_pwritev(fd, iov, iovcnt, offset);
if (part < 0)
return -1;
#ifdef SIMULATE_SHORT_WRITE
part = Min(part, 4096);
#endif
/* Count our progress. */
sum += part;
offset += part;
/* Step over iovecs that are done. */
while (iovcnt > 0 && iov->iov_len <= part)
{
part -= iov->iov_len;
++iov;
--iovcnt;
}
/* Are they all done? */
if (iovcnt == 0)
{
/* We don't expect the kernel to write more than requested. */
Assert(part == 0);
break;
}
/*
* Move whatever's left to the front of our mutable copy and adjust
* the leading iovec.
*/
Assert(iovcnt > 0);
memmove(iov_copy, iov, sizeof(*iov) * iovcnt);
Assert(iov->iov_len > part);
iov_copy[0].iov_base = (char *) iov_copy[0].iov_base + part;
iov_copy[0].iov_len -= part;
iov = iov_copy;
}
return sum;
}