From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57425) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1elF8m-0001wy-W7 for qemu-devel@nongnu.org; Mon, 12 Feb 2018 09:31:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1elF8i-00033N-Nt for qemu-devel@nongnu.org; Mon, 12 Feb 2018 09:31:33 -0500 Received: from mail-qk0-f170.google.com ([209.85.220.170]:44752) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1elF8i-000326-J7 for qemu-devel@nongnu.org; Mon, 12 Feb 2018 09:31:28 -0500 Received: by mail-qk0-f170.google.com with SMTP id n188so18553303qkn.11 for ; Mon, 12 Feb 2018 06:31:27 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20180212142506.28445-2-danielhb@linux.vnet.ibm.com> References: <20180212142506.28445-1-danielhb@linux.vnet.ibm.com> <20180212142506.28445-2-danielhb@linux.vnet.ibm.com> From: Marc-Andre Lureau Date: Mon, 12 Feb 2018 15:31:26 +0100 Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Daniel Henrique Barboza Cc: qemu-devel , marcandre , "Blake, Eric" , Yasmin Beatriz , Jose Ricardo Ziviani Hi On Mon, Feb 12, 2018 at 3:25 PM, Daniel Henrique Barboza wrote: > From: Yasmin Beatriz > > fd_write_vmcore can fail to execute for a lot of reasons that can be > retrieved by errno, but it only returns -1. This makes difficult for > the caller to know what happened and only a generic error message is > propagated back to the user. This is an example using dump-guest-memory: > > (qemu) dump-guest-memory /home/yasmin/mnt/test.dump > dump: failed to save memory > > All callers of fd_write_vmcore of dump.c does error handling via > error_setg(), so at first it seems feasible to add the Error pointer as > an argument of fd_write_vmcore. This proved to be more complex than it > first looked. fd_write_vmcore is used by write_elf64_notes and > write_elf32_notes as a WriteCoreDumpFunction prototype. WriteCoreDumpFunc= tion > is declared in include/qom/cpu.h and is used all around the code. This > leaves us with few alternatives: > > - change the WriteCoreDumpFunction prototype to include an error pointer. > This would require to change all functions that implements this prototype > to also receive an Error pointer; > > - change both write_elf64_notes and write_elf32_notes to no use the > WriteCoreDumpFunction. These functions use not only fd_write_vmcore > but also buf_write_note, so this would require to change buf_write_note > to handle an Error pointer. Considerable easier than the alternative > above, but it's still a lot of code just for the benefit of the callers > of fd_write_vmcore. > > This patch presents an easier solution that benefits all fd_write_vmcore > callers: > > - instead of returning -1 on error, return -errno. All existing callers > already checks for ret < 0 so there is no need to change the caller's > logic too much. This also allows the retrieval of the errno. > > - all callers were updated to use error_setg_errno instead of just > errno_setg. Now that fd_write_vmcore can return an errno, let's update > all callers so they can benefit from a more detailed error message. > > This is the same dump-guest-memory example with this patch applied: > > (qemu) dump-guest-memory /home/yasmin/mnt/test.dump > dump: failed to save memory: No space left on device > (qemu) > > This example illustrates an error of fd_write_vmcore when called > from write_data. All other callers will benefit from better > error messages as well. > > Reported-by: yilzhang@redhat.com > Cc: Jose Ricardo Ziviani > Signed-off-by: Yasmin Beatriz > Signed-off-by: Daniel Henrique Barboza lgtm, Reviewed-by: Marc-Andr=C3=A9 Lureau > --- > dump.c | 23 ++++++++++++++--------- > 1 file changed, 14 insertions(+), 9 deletions(-) > > diff --git a/dump.c b/dump.c > index 7b13baa413..171ff8a3b8 100644 > --- a/dump.c > +++ b/dump.c > @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, size_t si= ze, void *opaque) > > written_size =3D qemu_write_full(s->fd, buf, size); > if (written_size !=3D size) { > - return -1; > + return -errno; > } > > return 0; > @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, Error **= errp) > > ret =3D fd_write_vmcore(&elf_header, sizeof(elf_header), s); > if (ret < 0) { > - error_setg(errp, "dump: failed to write elf header"); > + error_setg_errno(errp, -ret, "dump: failed to write elf header")= ; > } > } > > @@ -171,7 +171,7 @@ static void write_elf32_header(DumpState *s, Error **= errp) > > ret =3D fd_write_vmcore(&elf_header, sizeof(elf_header), s); > if (ret < 0) { > - error_setg(errp, "dump: failed to write elf header"); > + error_setg_errno(errp, -ret, "dump: failed to write elf header")= ; > } > } > > @@ -194,7 +194,8 @@ static void write_elf64_load(DumpState *s, MemoryMapp= ing *memory_mapping, > > ret =3D fd_write_vmcore(&phdr, sizeof(Elf64_Phdr), s); > if (ret < 0) { > - error_setg(errp, "dump: failed to write program header table"); > + error_setg_errno(errp, -ret, > + "dump: failed to write program header table"); > } > } > > @@ -217,7 +218,8 @@ static void write_elf32_load(DumpState *s, MemoryMapp= ing *memory_mapping, > > ret =3D fd_write_vmcore(&phdr, sizeof(Elf32_Phdr), s); > if (ret < 0) { > - error_setg(errp, "dump: failed to write program header table"); > + error_setg_errno(errp, -ret, > + "dump: failed to write program header table"); > } > } > > @@ -237,7 +239,8 @@ static void write_elf64_note(DumpState *s, Error **er= rp) > > ret =3D fd_write_vmcore(&phdr, sizeof(Elf64_Phdr), s); > if (ret < 0) { > - error_setg(errp, "dump: failed to write program header table"); > + error_setg_errno(errp, -ret, > + "dump: failed to write program header table"); > } > } > > @@ -302,7 +305,8 @@ static void write_elf32_note(DumpState *s, Error **er= rp) > > ret =3D fd_write_vmcore(&phdr, sizeof(Elf32_Phdr), s); > if (ret < 0) { > - error_setg(errp, "dump: failed to write program header table"); > + error_setg_errno(errp, -ret, > + "dump: failed to write program header table"); > } > } > > @@ -355,7 +359,8 @@ static void write_elf_section(DumpState *s, int type,= Error **errp) > > ret =3D fd_write_vmcore(&shdr, shdr_size, s); > if (ret < 0) { > - error_setg(errp, "dump: failed to write section header table"); > + error_setg_errno(errp, -ret, > + "dump: failed to write section header table"); > } > } > > @@ -365,7 +370,7 @@ static void write_data(DumpState *s, void *buf, int l= ength, Error **errp) > > ret =3D fd_write_vmcore(buf, length, s); > if (ret < 0) { > - error_setg(errp, "dump: failed to save memory"); > + error_setg_errno(errp, -ret, "dump: failed to save memory"); > } else { > s->written_size +=3D length; > } > -- > 2.14.3 >