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9pfs: fix wrong I/O block size in Rgetattr 

When client sent a 9p Tgetattr request then the wrong I/O block
size value was returned by 9p server; instead of host file
system's I/O block size it should rather return an I/O block
size according to 9p session's 'msize' value, because the value
returned to client should be an "optimum" block size for I/O
(i.e. to maximize performance), it should not reflect the actual
physical block size of the underlying storage media.

The I/O block size of a host filesystem is typically 4k, so the
value returned was far too low for good 9p I/O performance.

This patch adds stat_to_iounit() with a similar approach as the
existing get_iounit() function.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <E1mT2Js-0000DW-OH@lizzy.crudebyte.com>
This commit is contained in:
Christian Schoenebeck 2021-09-22 15:13:31 +02:00
parent 931ce30859
commit 669ced09b3
1 changed files with 20 additions and 1 deletions
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21
hw/9pfs/9p.c
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@ -1262,6 +1262,25 @@ static int coroutine_fn stat_to_v9stat(V9fsPDU *pdu, V9fsPath *path,
#define P9_STATS_ALL 0x00003fffULL /* Mask for All fields above */
static int32_t stat_to_iounit(const V9fsPDU *pdu, const struct stat *stbuf)
{
int32_t iounit = 0;
V9fsState *s = pdu->s;
/*
* iounit should be multiples of st_blksize (host filesystem block size)
* as well as less than (client msize - P9_IOHDRSZ)
*/
if (stbuf->st_blksize) {
iounit = stbuf->st_blksize;
iounit *= (s->msize - P9_IOHDRSZ) / stbuf->st_blksize;
}
if (!iounit) {
iounit = s->msize - P9_IOHDRSZ;
}
return iounit;
}
static int stat_to_v9stat_dotl(V9fsPDU *pdu, const struct stat *stbuf,
V9fsStatDotl *v9lstat)
{
@ -1273,7 +1292,7 @@ static int stat_to_v9stat_dotl(V9fsPDU *pdu, const struct stat *stbuf,
v9lstat->st_gid = stbuf->st_gid;
v9lstat->st_rdev = stbuf->st_rdev;
v9lstat->st_size = stbuf->st_size;
v9lstat->st_blksize = stbuf->st_blksize;
v9lstat->st_blksize = stat_to_iounit(pdu, stbuf);
v9lstat->st_blocks = stbuf->st_blocks;
v9lstat->st_atime_sec = stbuf->st_atime;
v9lstat->st_atime_nsec = stbuf->st_atim.tv_nsec;