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[Qemu-devel] [PATCH v3 1/2] qga: flush explicitly when needed
From: |
marcandre . lureau |
Subject: |
[Qemu-devel] [PATCH v3 1/2] qga: flush explicitly when needed |
Date: |
Wed, 25 Nov 2015 13:59:11 +0100 |
From: Marc-André Lureau <address@hidden>
According to the specification:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html
"the application shall ensure that output is not directly followed by
input without an intervening call to fflush() or to a file positioning
function (fseek(), fsetpos(), or rewind()), and input is not directly
followed by output without an intervening call to a file positioning
function, unless the input operation encounters end-of-file."
Without this change, a write() followed by a read() may lose the
previously written content, as shown in the following test.
Fixes:
https://bugzilla.redhat.com/show_bug.cgi?id=1210246
---
qga/commands-posix.c | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 0ebd473..cf1d7ec 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -216,9 +216,16 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns,
Error **errp)
}
}
+typedef enum {
+ RW_STATE_NEW,
+ RW_STATE_READING,
+ RW_STATE_WRITING,
+} RwState;
+
typedef struct GuestFileHandle {
uint64_t id;
FILE *fh;
+ RwState state;
QTAILQ_ENTRY(GuestFileHandle) next;
} GuestFileHandle;
@@ -460,6 +467,17 @@ struct GuestFileRead *qmp_guest_file_read(int64_t handle,
bool has_count,
}
fh = gfh->fh;
+
+ /* explicitly flush when switching from writing to reading */
+ if (gfh->state == RW_STATE_WRITING) {
+ int ret = fflush(fh);
+ if (ret == EOF) {
+ error_setg_errno(errp, errno, "failed to flush file");
+ return NULL;
+ }
+ gfh->state = RW_STATE_NEW;
+ }
+
buf = g_malloc0(count+1);
read_count = fread(buf, 1, count, fh);
if (ferror(fh)) {
@@ -473,6 +491,7 @@ struct GuestFileRead *qmp_guest_file_read(int64_t handle,
bool has_count,
if (read_count) {
read_data->buf_b64 = g_base64_encode(buf, read_count);
}
+ gfh->state = RW_STATE_READING;
}
g_free(buf);
clearerr(fh);
@@ -496,6 +515,16 @@ GuestFileWrite *qmp_guest_file_write(int64_t handle, const
char *buf_b64,
}
fh = gfh->fh;
+
+ if (gfh->state == RW_STATE_READING) {
+ int ret = fseek(fh, 0, SEEK_CUR);
+ if (ret == -1) {
+ error_setg_errno(errp, errno, "failed to seek file");
+ return NULL;
+ }
+ gfh->state = RW_STATE_NEW;
+ }
+
buf = g_base64_decode(buf_b64, &buf_len);
if (!has_count) {
@@ -515,6 +544,7 @@ GuestFileWrite *qmp_guest_file_write(int64_t handle, const
char *buf_b64,
write_data = g_new0(GuestFileWrite, 1);
write_data->count = write_count;
write_data->eof = feof(fh);
+ gfh->state = RW_STATE_WRITING;
}
g_free(buf);
clearerr(fh);
@@ -538,10 +568,15 @@ struct GuestFileSeek *qmp_guest_file_seek(int64_t handle,
int64_t offset,
ret = fseek(fh, offset, whence);
if (ret == -1) {
error_setg_errno(errp, errno, "failed to seek file");
+ if (errno == ESPIPE) {
+ /* file is non-seekable, stdio shouldn't be buffering anyways */
+ gfh->state = RW_STATE_NEW;
+ }
} else {
seek_data = g_new0(GuestFileSeek, 1);
seek_data->position = ftell(fh);
seek_data->eof = feof(fh);
+ gfh->state = RW_STATE_NEW;
}
clearerr(fh);
@@ -562,6 +597,8 @@ void qmp_guest_file_flush(int64_t handle, Error **errp)
ret = fflush(fh);
if (ret == EOF) {
error_setg_errno(errp, errno, "failed to flush file");
+ } else {
+ gfh->state = RW_STATE_NEW;
}
}
--
2.5.0
- [Qemu-devel] [PATCH v3 0/2] qga: flush explicitly when needed, marcandre . lureau, 2015/11/25
- [Qemu-devel] [PATCH v3 1/2] qga: flush explicitly when needed,
marcandre . lureau <=
- [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, marcandre . lureau, 2015/11/25
- Re: [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, Eric Blake, 2015/11/25
- Re: [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, Michael Roth, 2015/11/25
- Re: [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, Eric Blake, 2015/11/25
- Re: [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, Michael Roth, 2015/11/25
- Re: [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, Eric Blake, 2015/11/25
- Re: [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, Michael Roth, 2015/11/25
- Re: [Qemu-devel] [PATCH v3 2/2] tests: add file-write-read test, Eric Blake, 2015/11/25