Hi Jamie,
On 11/11/21 15:11, Jamie Iles wrote:
> On Linux, read() will only ever read a maximum of 0x7ffff000 bytes
> regardless of what is asked. If the file is larger than 0x7ffff000
> bytes the read will need to be broken up into multiple chunks.
>
> Cc: Luc Michel <lmic...@kalray.eu>
> Signed-off-by: Jamie Iles <ja...@nuviainc.com>
> ---
> hw/core/loader.c | 40 ++++++++++++++++++++++++++++++++++------
> 1 file changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/hw/core/loader.c b/hw/core/loader.c
> index 348bbf535bd9..16ca9b99cf0f 100644
> --- a/hw/core/loader.c
> +++ b/hw/core/loader.c
> @@ -80,6 +80,34 @@ int64_t get_image_size(const char *filename)
> return size;
> }
>
> +static ssize_t read_large(int fd, void *dst, size_t len)
> +{
> + /*
> + * man 2 read says:
> + *
> + * On Linux, read() (and similar system calls) will transfer at most
> + * 0x7ffff000 (2,147,479,552) bytes, returning the number of bytes
Could you mention MAX_RW_COUNT from linux/fs.h?
> + * actually transferred. (This is true on both 32-bit and 64-bit
> + * systems.)
Maybe "This is true for both ILP32 and LP64 data models used by Linux"?
(because that would not be the case for the ILP64 model).
Otherwise s/systems/Linux variants/?
> + *
> + * So read in chunks no larger than 0x7ffff000 bytes.
> + */
> + size_t max_chunk_size = 0x7ffff000;
We can declare it static const.
> + size_t offset = 0;
> +
> + while (offset < len) {
> + size_t chunk_len = MIN(max_chunk_size, len - offset);
> + ssize_t br = read(fd, dst + offset, chunk_len);
> +
> + if (br < 0) {
> + return br;
> + }
> + offset += br;
> + }
> +
> + return (ssize_t)len;
> +}
I see other read()/pread() calls:
hw/9pfs/9p-local.c:472: tsize = read(fd, (void *)buf, bufsz);
hw/vfio/common.c:269: if (pread(vbasedev->fd, &buf, size,
region->fd_offset + addr) != size) {
...
Maybe the read_large() belongs to "sysemu/os-xxx.h"?
