From: Max Reitz <mreitz@redhat.com>
To: Denis Plotnikov <dplotnikov@virtuozzo.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v9] qemu-io: add pattern file for write command
Date: Tue, 20 Aug 2019 15:35:13 +0200 [thread overview]
Message-ID: <f3eb6ae0-98d9-b7d1-3c04-60b37444fa68@redhat.com> (raw)
In-Reply-To: <20190819161811.15872-1-dplotnikov@virtuozzo.com>
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On 19.08.19 18:18, Denis Plotnikov wrote:
> The patch allows to provide a pattern file for write
> command. There was no similar ability before.
>
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---
> v9:
> * replace flag cast to int with bool [Eric]
> * fix the error message [Eric]
> * use qemu_io_free instead of qemu_vfree [Eric]
> * add function description [Eric]
>
> v8: fix according to Max's comments
> * get rid of unnecessary buffer for the pattern
> * buffer allocation just in bytes
> * take into account the missalign offset
> * don't copy file name
> * changed char* to const char* in input params
>
> v7:
> * fix variable naming
> * make code more readable
> * extend help for write command
>
> v6:
> * the pattern file is read once to reduce io
>
> v5:
> * file name initiated with null to make compilers happy
>
> v4:
> * missing signed-off clause added
>
> v3:
> * missing file closing added
> * exclusive flags processing changed
> * buffer void* converted to char* to fix pointer arithmetics
> * file reading error processing added
> ---
> qemu-io-cmds.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 91 insertions(+), 6 deletions(-)
>
> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> index 09750a23ce..f7bdfe673b 100644
> --- a/qemu-io-cmds.c
> +++ b/qemu-io-cmds.c
> @@ -351,6 +351,77 @@ static void qemu_io_free(void *p)
> qemu_vfree(p);
> }
>
> +/*
> + * qemu_io_alloc_from_file()
> + *
> + * Allocates the buffer and populates it with the content of the given file
> + * up to @len bytes. If the file length is less then @len, then the buffer
s/then/than/ (the first one)
> + * is populated with then file content cyclically.
s/then/the/
> + *
> + * @blk - the block backend where the buffer content is going to be written to
> + * @len - the buffer length
> + * @file_name - the file to copy the content from
Probably better s/copy/read/
> + *
> + * Returns: the buffer pointer on success
> + * NULL on error
> + */
> +static void *qemu_io_alloc_from_file(BlockBackend *blk, size_t len,
> + const char *file_name)
> +{
> + char *buf, *buf_origin;
> + FILE *f = fopen(file_name, "r");
> + int pattern_len;
> +
> + if (!f) {
> + perror(file_name);
> + return NULL;
> + }
> +
> + if (qemuio_misalign) {
> + len += MISALIGN_OFFSET;
> + }
> +
> + buf_origin = buf = blk_blockalign(blk, len);
> +
> + if (qemuio_misalign) {
> + buf_origin += MISALIGN_OFFSET;
> + }
> +
> + pattern_len = fread(buf_origin, 1, len, f);
Pulling the misalignment up here has more effects than just requiring
qemu_io_free() rather than qemu_vfree().
First, it breaks this fread(), because @len is the length of the buffer
in total, so this here is a buffer overflow.
> +
> + if (ferror(f)) {
> + perror(file_name);
> + goto error;
> + }
> +
> + if (pattern_len == 0) {
> + fprintf(stderr, "%s: file is empty\n", file_name);
> + goto error;
> + }
> +
> + fclose(f);
> +
> + if (len > pattern_len) {
> + len -= pattern_len;
> + buf += pattern_len;
> +
> + while (len > 0) {
> + size_t len_to_copy = MIN(pattern_len, len);
> +
> + memcpy(buf, buf_origin, len_to_copy);
Second, it breaks this memcpy(), because now [buf, buf + len_to_copy)
and [buf_origin, buf_origin + len_to_copy) may overlap.
I think the solution would be (1) to add MISALIGN_OFFSET not only to
@buf_origin, but to @buf also, and (2) to reduce len by MISALIGN_OFFSET.
So all in all, I think both issues should be fixed if you add
“buf += MISALIGN_OFFSET” and “len -= MISALIGN_OFFSET” to the second
“if (qemuio_misalign)” block. I think.
> +
> + len -= len_to_copy;
> + buf += len_to_copy;
> + }
> + }
> +
> + return buf_origin;
> +
> +error:
> + qemu_io_free(buf_origin);
> + return NULL;
> +}
> +
> static void dump_buffer(const void *buffer, int64_t offset, int64_t len)
> {
> uint64_t i;
[...]
> @@ -1051,8 +1128,9 @@ static int write_f(BlockBackend *blk, int argc, char **argv)
> return -EINVAL;
> }
>
> - if (zflag && Pflag) {
> - printf("-z and -P cannot be specified at the same time\n");
> + if ((bool)zflag + (bool)Pflag + (bool)sflag > 1) {
Eric’s point was that you don’t need to cast at all.
Max
> + printf("Only one of -z, -P, and -s "
> + "can be specified at the same time\n");
> return -EINVAL;
> }
>
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next prev parent reply other threads:[~2019-08-20 13:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 16:18 [Qemu-devel] [PATCH v9] qemu-io: add pattern file for write command Denis Plotnikov
2019-08-20 13:35 ` Max Reitz [this message]
2019-08-20 16:24 ` Denis Plotnikov
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