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When performing a base backup, check for read errors.

The old code didn't differentiate between a read error and aconcurrent 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 notsure that would qualify as a back-patchable bug fix, so just dothis much for now.Jeevan Chalke, reviewed by Jeevan Ladhe and by me.Discussion:http://postgr.es/m/CA+TgmobG4ywMzL5oQq2a8YKp8x2p3p1LOMMcGqpS7aekT9+ETA@mail.gmail.com

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src/backend/replication
- basebackup.c

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`‎src/backend/replication/basebackup.c`

Lines changed: 31 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -90,6 +90,18 @@ static char *statrelpath = NULL;`
`90`	`90`	`*/`
`91`	`91`	`#defineTHROTTLING_FREQUENCY8`
`92`	`92`
	`93`	`+/*`
	`94`	`+ * Checks whether we encountered any error in fread(). fread() doesn't give`
	`95`	`+ * any clue what has happened, so we check with ferror(). Also, neither`
	`96`	`+ * fread() nor ferror() set errno, so we just throw a generic error.`
	`97`	`+ */`
	`98`	`+#defineCHECK_FREAD_ERROR(fp,filename) \`
	`99`	`+do { \`
	`100`	`+if (ferror(fp)) \`
	`101`	`+ereport(ERROR, \`
	`102`	`+(errmsg("could not read from file \"%s\"", filename))); \`
	`103`	`+} while (0)`
	`104`	`+`
`93`	`105`	`/* The actual number of bytes, transfer of which may cause sleep. */`
`94`	`106`	`staticuint64throttling_sample;`
`95`	`107`
`@@ -543,6 +555,8 @@ perform_base_backup(basebackup_options *opt)`
`543`	`555`	`break;`
`544`	`556`	`}`
`545`	`557`
	`558`	`+CHECK_FREAD_ERROR(fp,pathbuf);`
	`559`	`+`
`546`	`560`	`if (len!=wal_segment_size)`
`547`	`561`	`{`
`548`	`562`	`CheckXLogRemoved(segno,tli);`
`@@ -1478,6 +1492,20 @@ sendFile(const char readfilename, const char tarfilename, struct stat *statbuf`
`1478`	`1492`
`1479`	`1493`	`if (fread(buf+BLCKSZ*i,1,BLCKSZ,fp)!=BLCKSZ)`
`1480`	`1494`	`{`
	`1495`	`+/*`
	`1496`	`+ * If we hit end-of-file, a concurrent`
	`1497`	`+ * truncation must have occurred, so break out`
	`1498`	`+ * of this loop just as if the initial fread()`
	`1499`	`+ * returned 0. We'll drop through to the same`
	`1500`	`+ * code that handles that case. (We must fix`
	`1501`	`+ * up cnt first, though.)`
	`1502`	`+ */`
	`1503`	`+if (feof(fp))`
	`1504`	`+{`
	`1505`	`+cnt=BLCKSZ*i;`
	`1506`	`+break;`
	`1507`	`+}`
	`1508`	`+`
`1481`	`1509`	`ereport(ERROR,`
`1482`	`1510`	`(errcode_for_file_access(),`
`1483`	`1511`	`errmsg("could not reread block %d of file \"%s\": %m",`
`@@ -1529,7 +1557,7 @@ sendFile(const char readfilename, const char tarfilename, struct stat *statbuf`
`1529`	`1557`	`len+=cnt;`
`1530`	`1558`	`throttle(cnt);`
`1531`	`1559`
`1532`		`-if (len >=statbuf->st_size)`
	`1560`	`+if (feof(fp)\|\|len >=statbuf->st_size)`
`1533`	`1561`	`{`
`1534`	`1562`	`/*`
`1535`	`1563`	`* Reached end of file. The file could be longer, if it was`
`@@ -1540,6 +1568,8 @@ sendFile(const char readfilename, const char tarfilename, struct stat *statbuf`
`1540`	`1568`	`}`
`1541`	`1569`	`}`
`1542`	`1570`
	`1571`	`+CHECK_FREAD_ERROR(fp,readfilename);`
	`1572`	`+`
`1543`	`1573`	`/* If the file was truncated while we were sending it, pad it with zeros */`
`1544`	`1574`	`if (len<statbuf->st_size)`
`1545`	`1575`	`{`

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`‎src/backend/replication/basebackup.c`

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