Fix sign-compare warnings in pg_iovec.h.

nathan-bossart · nathan-bossart · commit 0a883a067bd7 · 2024-11-08T16:11:08.000-06:00
The code in question (pg_preadv() and pg_pwritev()) has been around for a while, but commit 15c9ac3 moved it to a header file. If third-party code that includes this header file is built with -Wsign-compare on a system without preadv() or pwritev(), warnings ensue. This commit fixes said warnings by casting the result of pg_pread()/pg_pwrite() to size_t, which should be safe because we will have already checked for a negative value. Author: Wolfgang Walther Discussion: https://postgr.es/m/16989737-1aa8-48fd-8dfe-b7ada06509ab%40technowledgy.de Backpatch-through: 17
diff --git a/src/include/port/pg_iovec.h b/src/include/port/pg_iovec.h
@@ -68,7 +68,7 @@ pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
 		}
 		sum += part;
 		offset += part;
-		if (part < iov[i].iov_len)
+		if ((size_t) part < iov[i].iov_len)
 			return sum;
 	}
 	return sum;
@@ -107,7 +107,7 @@ pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)
 		}
 		sum += part;
 		offset += part;
-		if (part < iov[i].iov_len)
+		if ((size_t) part < iov[i].iov_len)
 			return sum;
 	}
 	return sum;

Original file line number	Diff line number	Diff line change
`@@ -68,7 +68,7 @@ pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)`
`68`	`68`	`}`
`69`	`69`	`sum += part;`
`70`	`70`	`offset += part;`
`71`		`- if (part < iov[i].iov_len)`
	`71`	`+ if ((size_t) part < iov[i].iov_len)`
`72`	`72`	`return sum;`
`73`	`73`	`}`
`74`	`74`	`return sum;`
`@@ -107,7 +107,7 @@ pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)`
`107`	`107`	`}`
`108`	`108`	`sum += part;`
`109`	`109`	`offset += part;`
`110`		`- if (part < iov[i].iov_len)`
	`110`	`+ if ((size_t) part < iov[i].iov_len)`
`111`	`111`	`return sum;`
`112`	`112`	`}`
`113`	`113`	`return sum;`