| Message ID | 20180720214020.22897-4-bsd@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Jul 20, 2018 at 05:40:18PM -0400, Bandan Das wrote: > For large buffers, write may not copy the full buffer. For example, > on Linux, write imposes a limit of 0x7ffff000. Note that this does > not fix >4G transfers but ~>2G files will transfer successfully. Hmm, I guess it would be a good idea to write the file in smaller pieces, so we don't need a 2G host buffer to let the guest write a 2G file ... (as incremental improvement on top of this series). cheers, Gerd
Gerd Hoffmann <kraxel@redhat.com> writes: > On Fri, Jul 20, 2018 at 05:40:18PM -0400, Bandan Das wrote: >> For large buffers, write may not copy the full buffer. For example, >> on Linux, write imposes a limit of 0x7ffff000. Note that this does >> not fix >4G transfers but ~>2G files will transfer successfully. > > Hmm, I guess it would be a good idea to write the file in smaller > pieces, so we don't need a 2G host buffer to let the guest write > a 2G file ... > > (as incremental improvement on top of this series). > Sounds good, I will add this to my todo list. > cheers, > Gerd
On 2018-07-20 23:40, Bandan Das wrote: > For large buffers, write may not copy the full buffer. For example, > on Linux, write imposes a limit of 0x7ffff000. Note that this does > not fix >4G transfers but ~>2G files will transfer successfully. > > Signed-off-by: Bandan Das <bsd@redhat.com> > --- > hw/usb/dev-mtp.c | 22 ++++++++++++++++++++-- > 1 file changed, 20 insertions(+), 2 deletions(-) > > diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c > index 1b72603dc5..c8f6eb4e9e 100644 > --- a/hw/usb/dev-mtp.c > +++ b/hw/usb/dev-mtp.c > @@ -1602,6 +1602,24 @@ static void utf16_to_str(uint8_t len, uint16_t *arr, char *name) > g_free(wstr); > } > > +/* Wrapper around write, returns 0 on failure */ > +static uint64_t write_retry(int fd, void *buf, uint64_t size) > +{ > + uint64_t bytes_left = size, ret; > + > + while (bytes_left > 0) { > + ret = write(fd, buf, bytes_left); > + if ((ret == -1) && (errno != EINTR || errno != EAGAIN || > + errno != EWOULDBLOCK)) { Someone opened a bug ticket about this here: https://bugs.launchpad.net/qemu/+bug/1798780 The check looks wrong, indeed - either "!=" should be "==" or "||" should be "&&" here ? Thomas
diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c index 1b72603dc5..c8f6eb4e9e 100644 --- a/hw/usb/dev-mtp.c +++ b/hw/usb/dev-mtp.c @@ -1602,6 +1602,24 @@ static void utf16_to_str(uint8_t len, uint16_t *arr, char *name) g_free(wstr); } +/* Wrapper around write, returns 0 on failure */ +static uint64_t write_retry(int fd, void *buf, uint64_t size) +{ + uint64_t bytes_left = size, ret; + + while (bytes_left > 0) { + ret = write(fd, buf, bytes_left); + if ((ret == -1) && (errno != EINTR || errno != EAGAIN || + errno != EWOULDBLOCK)) { + break; + } + bytes_left -= ret; + buf += ret; + } + + return size - bytes_left; +} + static void usb_mtp_write_data(MTPState *s) { MTPData *d = s->data_out; @@ -1644,8 +1662,8 @@ static void usb_mtp_write_data(MTPState *s) goto success; } - rc = write(d->fd, d->data, s->dataset.size); - if (rc == -1) { + rc = write_retry(d->fd, d->data, s->dataset.size); + if (!rc) { usb_mtp_queue_result(s, RES_STORE_FULL, d->trans, 0, 0, 0, 0); goto done;
For large buffers, write may not copy the full buffer. For example, on Linux, write imposes a limit of 0x7ffff000. Note that this does not fix >4G transfers but ~>2G files will transfer successfully. Signed-off-by: Bandan Das <bsd@redhat.com> --- hw/usb/dev-mtp.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-)