Re: [PATCH 3/3] vmcore: Convert read_from_oldmem() to take an iov_iter
From: Matthew Wilcox <willy@infradead.org>
Date: 2021-12-13 13:42:45
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On Mon, Dec 13, 2021 at 09:02:57AM +0100, Christoph Hellwig wrote:
quoted
ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos) { - return read_from_oldmem(buf, count, ppos, 0, + struct kvec kvec = { .iov_base = buf, .iov_len = count }; + struct iov_iter iter; + + iov_iter_kvec(&iter, READ, &kvec, 1, count); + + return read_from_oldmem(&iter, count, ppos, cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)); }elfcorehdr_read should probably also take an iov_iter while we're at it.
I don't like how that looks. For example:
@@ -1246,11 +1247,14 @@ static int __init parse_crash_elf64_headers(void) int rc=0; Elf64_Ehdr ehdr; u64 addr; + struct iov_iter iter; + struct kvec kvec = { .iov_base = &ehdr, .iov_len = sizeof(ehdr) }; addr = elfcorehdr_addr; /* Read Elf header */ - rc = elfcorehdr_read((char *)&ehdr, sizeof(Elf64_Ehdr), &addr); + iov_iter_kvec(&iter, READ, &kvec, 1, sizeof(ehdr)); + rc = elfcorehdr_read(&iter, &addr); if (rc < 0) return rc;
@@ -1277,7 +1281,10 @@ static int __init parse_crash_elf64_headers(void) if (!elfcorebuf) return -ENOMEM; addr = elfcorehdr_addr; - rc = elfcorehdr_read(elfcorebuf, elfcorebuf_sz_orig, &addr); + kvec.iov_base = elfcorebuf; + kvec.iov_len = elfcorebuf_sz_orig; + iov_iter_kvec(&iter, READ, &kvec, 1, elfcorebuf_sz_orig); + rc = elfcorehdr_read(&iter, &addr); if (rc < 0) goto fail;
I don't think this makes the code clearer, and it's already pretty ugly code. I'd rather leave constructing the iov_iter to elfcorehdr_read(). (Same remarks apply to elfcorehdr_read_notes())
I also don't quite understand why we even need the arch overrides for it, but that would require some digging into the history of this interface.
I decided I didn't want to know ;-)