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Re: [Qemu-block] [Qemu-devel] [PATCH v7] pflash: Require backend size to

From: Markus Armbruster
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v7] pflash: Require backend size to match device, improve errors
Date: Fri, 08 Mar 2019 15:29:13 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Kevin Wolf <address@hidden> writes:

> Am 08.03.2019 um 13:28 hat Markus Armbruster geschrieben:
>> Laszlo Ersek <address@hidden> writes:
>> > This one has got to be one of the longest bike-shedding sessions! :)
>> >
>> > I'm fine with this patch, but I could suggest two improvements.
>> >
>> > (1) When blk_getlength() fails, we could format the negative error code
>> > returned by it into the error message.
>> I can do that.
> By using error_setg_errno(), I assume. Not throwing away error details
> is always good.
>> > (2) We could extract the common code to a new function in
>> > "hw/block/block.c". (It says "Common code for block device models" on
>> > the tin.)
>> There's so much common code in these two files even before this patch...
> My understanding is that hw/block/block.c contains code that is
> potentially useful to all kinds of block devices, not random code that
> two specific similar devices happen to share.
> If we want to deduplicate some code in the flash devices, without any
> expectation that other devices will use it at some point, I'd rather
> create a new source file hw/block/pflash_common.c or something like
> that.


The helper I came up with (appended) isn't really specific to flash
devices.  Would it be okay for hw/block/block.c even though only the two
flash devices use it for now?

bool blk_check_size_and_read_all(BlockBackend *blk, void *buf, hwaddr size,
                                 Error **errp)
    int64_t blk_len;
    int ret;

    blk_len = blk_getlength(blk);
    if (blk_len < 0) {
        error_setg_errno(errp, -blk_len,
                         "can't get size of block backend '%s'",
        return false;
    if (blk_len != size) {
        error_setg(errp, "device requires %" PRIu64 " bytes, "
                   "block backend '%s' provides %" PRIu64 " bytes",
                   size, blk_name(blk), blk_len);
        return false;

    /* TODO for @size > BDRV_REQUEST_MAX_BYTES, we'd need to loop */
    assert(size <= BDRV_REQUEST_MAX_BYTES);
    ret = blk_pread(blk, 0, buf, size);
    if (ret < 0) {
        error_setg_errno(errp, -ret, "can't read block backend '%s'",
        return false;
    return true;

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