On Tue, 25 Jan 2011, Yauheni Kaliuta wrote:
> Hi!
>
> On Tue, Jan 25, 2011 at 10:02 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> > On Tue, 25 Jan 2011, Yauheni Kaliuta wrote:
> >
> >> Hi!
> >>
> >> file_storage.c has the following code in do_write():
>
> [...]
>
> >> Â Â Â Â Â Â Â Â Â Â Â Â /* If an error occurred, report it and its position */
> >> Â Â Â Â Â Â Â Â Â Â Â Â if (nwritten < amount) {
> >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â curlun->sense_data = SS_WRITE_ERROR;
> >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â curlun->sense_data_info = file_offset >> 9;
> >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â curlun->info_valid = 1;
> >> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â break;
> >> Â Â Â Â Â Â Â Â Â Â Â Â }
> >>
> >> In case of some data written (nwritten > 0), shouldn't it try to write
> >> the rest before error reporting?
> >
> > In theory, perhaps it should. Â I haven't run across any situations
> > where nwritten was > 0 and < amount. Â Likewise with reading.
> >
>
> Well, I'm lucky enough to get it :) Not with the upstream code,
> however, but with custom read/write functions (which avoid vfs layer).
Here's a patch I wrote some time ago but never submitted because it
didn't seem necessary. It may need some adjustment before you can
apply it to a current kernel.
Alan Stern
Index: usb-2.6/drivers/usb/gadget/file_storage.c
===================================================================
--- usb-2.6.orig/drivers/usb/gadget/file_storage.c
+++ usb-2.6/drivers/usb/gadget/file_storage.c
@@ -1132,7 +1132,7 @@ static int do_read(struct fsg_dev *fsg)
int rc;
u32 amount_left;
loff_t file_offset, file_offset_tmp;
- unsigned int amount;
+ unsigned int amount, buf_offset;
unsigned int partial_page;
ssize_t nread;
@@ -1200,10 +1200,12 @@ static int do_read(struct fsg_dev *fsg)
break;
}
+ buf_offset = 0;
+ continue_read:
/* Perform the read */
file_offset_tmp = file_offset;
nread = vfs_read(curlun->filp,
- (char __user *) bh->buf,
+ buf_offset + (char __user *) bh->buf,
amount, &file_offset_tmp);
VLDBG(curlun, "file read %u @ %llu -> %d\n", amount,
(unsigned long long) file_offset,
@@ -1223,11 +1225,17 @@ static int do_read(struct fsg_dev *fsg)
file_offset += nread;
amount_left -= nread;
fsg->residue -= nread;
- bh->inreq->length = nread;
+ buf_offset += nread;
+ bh->inreq->length = buf_offset;
bh->state = BUF_STATE_FULL;
/* If an error occurred, report it and its position */
if (nread < amount) {
+ /* Continue after a partial read */
+ if (nread > 0) {
+ amount -= nread;
+ goto continue_read;
+ }
curlun->sense_data = SS_UNRECOVERED_READ_ERROR;
curlun->sense_data_info = file_offset >> 9;
curlun->info_valid = 1;
@@ -1258,7 +1266,7 @@ static int do_write(struct fsg_dev *fsg)
int get_some_more;
u32 amount_left_to_req, amount_left_to_write;
loff_t usb_offset, file_offset, file_offset_tmp;
- unsigned int amount;
+ unsigned int amount, buf_offset;
unsigned int partial_page;
ssize_t nwritten;
int rc;
@@ -1387,10 +1395,12 @@ static int do_write(struct fsg_dev *fsg)
amount = curlun->file_length - file_offset;
}
+ buf_offset = 0;
+ continue_write:
/* Perform the write */
file_offset_tmp = file_offset;
nwritten = vfs_write(curlun->filp,
- (char __user *) bh->buf,
+ buf_offset + (char __user *) bh->buf,
amount, &file_offset_tmp);
VLDBG(curlun, "file write %u @ %llu -> %d\n", amount,
(unsigned long long) file_offset,
@@ -1408,12 +1418,18 @@ static int do_write(struct fsg_dev *fsg)
nwritten -= (nwritten & 511);
// Round down to a block
}
- file_offset += nwritten;
+ file_offset += nwritten;
amount_left_to_write -= nwritten;
fsg->residue -= nwritten;
+ buf_offset += nwritten;
/* If an error occurred, report it and its position */
if (nwritten < amount) {
+ /* Continue after a partial write */
+ if (nwritten > 0) {
+ amount -= nwritten;
+ goto continue_write;
+ }
curlun->sense_data = SS_WRITE_ERROR;
curlun->sense_data_info = file_offset >> 9;
curlun->info_valid = 1;
--
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