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When performing a base backup, check for read errors.

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The old code didn't differentiate between a read error and a
concurrent truncation. fread reports both of these by returning 0;
you have to use feof() or ferror() to distinguish between them,
which this code did not do.

It might be a better idea to use read() rather than fread() here,
so that we can display a less-generic error message, but I'm not
sure that would qualify as a back-patchable bug fix, so just do
this much for now.

Jeevan Chalke, reviewed by Jeevan Ladhe and by me.

Discussion: http://postgr.es/m/CA+TgmobG4ywMzL5oQq2a8YKp8x2p3p1LOMMcGqpS7aekT9+ETA@mail.gmail.com
This commit is contained in:
Robert Haas 2019-09-06 08:22:32 -04:00
parent af28744288
commit 61c65cce40
1 changed files with 31 additions and 1 deletions
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32
src/backend/replication/basebackup.c
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@ -90,6 +90,18 @@ static char *statrelpath = NULL;
*/ */
#define THROTTLING_FREQUENCY 8 #define THROTTLING_FREQUENCY 8
/*
* Checks whether we encountered any error in fread(). fread() doesn't give
* any clue what has happened, so we check with ferror(). Also, neither
* fread() nor ferror() set errno, so we just throw a generic error.
*/
#define CHECK_FREAD_ERROR(fp, filename) \
do { \
if (ferror(fp)) \
ereport(ERROR, \
(errmsg("could not read from file \"%s\"", filename))); \
} while (0)
/* The actual number of bytes, transfer of which may cause sleep. */ /* The actual number of bytes, transfer of which may cause sleep. */
static uint64 throttling_sample; static uint64 throttling_sample;
@ -550,6 +562,8 @@ perform_base_backup(basebackup_options *opt)
break; break;
} }
CHECK_FREAD_ERROR(fp, pathbuf);
if (len != wal_segment_size) if (len != wal_segment_size)
{ {
CheckXLogRemoved(segno, tli); CheckXLogRemoved(segno, tli);
@ -1487,6 +1501,20 @@ sendFile(const char *readfilename, const char *tarfilename, struct stat *statbuf
if (fread(buf + BLCKSZ * i, 1, BLCKSZ, fp) != BLCKSZ) if (fread(buf + BLCKSZ * i, 1, BLCKSZ, fp) != BLCKSZ)
{ {
/*
* If we hit end-of-file, a concurrent
* truncation must have occurred, so break out
* of this loop just as if the initial fread()
* returned 0. We'll drop through to the same
* code that handles that case. (We must fix
* up cnt first, though.)
*/
if (feof(fp))
{
cnt = BLCKSZ * i;
break;
}
ereport(ERROR, ereport(ERROR,
(errcode_for_file_access(), (errcode_for_file_access(),
errmsg("could not reread block %d of file \"%s\": %m", errmsg("could not reread block %d of file \"%s\": %m",
@ -1538,7 +1566,7 @@ sendFile(const char *readfilename, const char *tarfilename, struct stat *statbuf
len += cnt; len += cnt;
throttle(cnt); throttle(cnt);
if (len >= statbuf->st_size) if (feof(fp) || len >= statbuf->st_size)
{ {
/* /*
* Reached end of file. The file could be longer, if it was * Reached end of file. The file could be longer, if it was
@ -1549,6 +1577,8 @@ sendFile(const char *readfilename, const char *tarfilename, struct stat *statbuf
} }
} }
CHECK_FREAD_ERROR(fp, readfilename);
/* If the file was truncated while we were sending it, pad it with zeros */ /* If the file was truncated while we were sending it, pad it with zeros */
if (len < statbuf->st_size) if (len < statbuf->st_size)
{ {